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The Best 300-Gallon Deck Boxes of 2026: Two Shells, Nine Labels, and the One Box Bigger Than Its Number

By The Smith Family, reviewed by Brad Smith · Independent, no paid placement · Updated October 30, 2026Prices checked September 2026

Some links here are affiliate links — if you buy through them, we may earn a commission at no extra cost to you (sometimes with a discount for you). It never changes which products we recommend — and we name the SKIPs to prove it.

Search “320 gallon deck box” and Google finishes the sentence for you: Costco, Home Depot, Walmart, waterproof, brown, black. The demand is real. What is not real is most of the number. We read every 300-gallon-plus deck box on Amazon’s best-seller and new-release lists and three searches, signed in, on 17 September 2026, with the critical reviews read for each of the five we carded — and then we did the one thing no roundup does: we divided each box’s own listed dimensions by 231, the cubic inches in a gallon.

The class is two resin shells. One measures 67.72 × 32.2 × 33.66 inches on four different brands’ listings and holds 318 gallons of exterior volume; it is sold as 320, 330, 350 and 370. The other is about 58 × 32 × 34 inches, 272 gallons of exterior, sold as 300, 320 and 380. Only one box in the class is bigger than its label. That is the box we would buy, and its catches are printed below the buy button.

How they compare

Model	Best for	Showdown Score ↕	Capacity	Exterior volume	Material	Lid	Warranty	Price
NUNU LAB 320 Gallon Deck Box	Best overall (the only shell bigger than its label)	6.0 Good	320 gal (listing)	376 gal (75.08 × 34.37 × ~33.7 in; the listing's own height field reads 6.69 in, a data error)	Resin (listing)	Piston-assisted, lockable (lock not included)	Not published	Check price →
YITAHOME 300 Gallon Double-Wall Deck Box	Best build on paper — and sold by Amazon	5.5 Good	300 gal (listing)	291 gal (60.6 × 33.5 × 33.1 in)	Double-wall resin (listing)	Gas struts, soft-close, lockable (lock not included)	1 year limited, bought direct from Yitahome only; excludes outdoor use unless expressly stated	Soon
MIRADOR 281 Gallon Aluminum Deck Box (Horizon)	The metal one, from a maker that exists	5.6 Good	281 gal (listing and maker)	340 gal (71.7 × 35.2 × 31.1 in)	Aluminum and steel, powder-coated (listing)	Soft-close pistons, lockable	15 years from the original purchase date, original owner and registrant (Mirador deck box warranty, 2026/02)	Check price →
TARKARI 370 Gallon Deck Box	SKIP	6.1 Good	370 gal (listing)	318 gal (67.72 × 32.2 × 33.66 in) — the label exceeds the box	Resin (listing)	Hydraulic, lockable (lock not included)	Not published	Check price →

Prices move constantly — any Amazon price shown is as of the date noted and subject to change; tap through for today's number.

Two shells, nine labels

Every resin box in the 300-plus class carries an “Item Dimensions” line in its Amazon detail table. We read them side by side. Then we multiplied.

Exterior volume is the most a box could hold if it had no walls and no lid. A real interior is smaller. So a label at 100% or more of the exterior is not an estimate; it is a number that cannot be true. Seven of the eleven are over. The two that are under — NUNU LAB and MIRADOR — are the two we rank first and third, and the third-party research we commissioned before reading the listings found the first shell sold under two more badges, LAUSAINT HOME on Amazon and ACOINEL at Target, at the same hundredth of an inch.

The seller column is the tell for who is who. ARTS BOX US sells the first shell as TARKARI 370 and as Yardgrace 320, and the second shell as Yardgrace 300. ATMELT and EFU print the same manufacturer part number, 248A, on boxes labelled 300 and 380. None of the resin brands on this table has a website: nunulab.com, atmelt.com and tarkari.com all redirect to a parked lander, kamaboko.com is a Japanese fish-cake company, and the one that does exist — yardgrace.com — is the same operation as TARKARI by seller. YITAHOME’s site answered 503 all day. Mirador’s store is real, sells the 281 direct for less than Amazon does, and lists a 370-gallon Urban above it that is not on Amazon at all.

Read again on 28 October: more labels on the same shell

When the ATMELT went unavailable we read the class again, signed in, on 28 October 2026: six searches, page two, the most-reviewed sort, a $150–$300 price band and both of Amazon’s Deck Boxes lists. Seven more listings, through the same arithmetic.

The 272-gallon shell now wears three more badges, and two boxes carry a label twice their own exterior. The last column is why none of them took the ATMELT’s slot. Each listing’s star average pools every size it sells, from 30 or 35 gallons up; reviews of the size in the title number zero to eight. Our floor for carding a box is 50 ratings of its own, so we retired the best-value slot instead of filling it with a small bin’s reputation. The YITAHOME 320 Double-Wall, the one box Amazon itself sells near this size, has the same problem: eight written reviews of the 320, four of them one or two stars, most for a lid that warped.

The three failures, and they are the same as the 150-gallon class

Our large-deck-box page found that a resin box fails three ways — a lid that lets water in when opened, hinges that snap, and a shell that warps. The 300-plus tails add nothing new; they add scale. A 68-inch snap-together panel bows more than a 60-inch one. Owners of four of the five boxes we carded in September describe walls that bulge under cushions alone, bottoms that pull away from the sides when the box is pushed, and pieces that “do not clearly and positively snap together as instructions state”. Two describe wind: the TARKARI “blew apart in a wind storm”; the NUNU LAB’s lid “blew open and the plastic snapped all the hinges”. The MIRADOR, being metal, fails differently — bent panels out of the box and screw holes that will not line up.

Read those with the base composition in mind. Every rating on this page pools a size ladder: the NUNU LAB’s 1,182 ratings span boxes from 30 gallons up, and reviews of 33- and 35-gallon units sit on the 320’s own critical page. The star average is the family’s, not the big box’s.

Best overall: NUNU LAB 320 Gallon Deck Box

Winner

Our top pick

NUNU LAB 320 Gallon Deck Box

Best overall (the only shell bigger than its label)

Showdown Score™

6.0

Good

Good is 5.5 to 6.4.

Likely 4.4 to 7.6

See why it scored 6.0

Low confidence

Low confidence: part of the evidence is unread or thin. The margin is ±1.6, so the true score is likely 4.4 to 7.6.

Owners1,182 Amazon ratings, read 2.5Failure recordRead from the owner base3.5Hands-on testNo credentialed test yet. A missing test never costs points.None yetTotal6.0

Too close to call with the TARKARI 370 Gallon Deck Box, which scores 6.1. It holds "Best overall" because its owner rating is deeper (1,182 vs 211 of its own ratings).

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The largest box of the class, 75 inches long, and the only one whose gallon figure fits inside its own dimensions, on the deepest base of the class (4.3★/1,182, pooled across 29 sizes and colours). The seller of record is a Ningbo storefront named 'Amzaon''. Owners describe walls that bow when loaded and a lid a windstorm opens.

Sold in 29 sizes and colours on this listing (30–320 gal) — this card is the 320 gal, Rattan Black. Check the size before you add to cart.

Your pick if you want the biggest box in the class and you have checked who is selling it: 75 by 34 inches of resin, a 4.3★/1,182 base, and the one 300-gallon-plus claim on Amazon that fits inside the box's own exterior volume (376 gallons). Not for you if a lid that can blow open in wind is a deal-breaker — that is its tail.

4.3 · 1,182 owner ratingsacross Amazon · September 2026 · listing-wide base

Check price at Amazon →

Picked before we checked what this link pays us.

NUNU LAB 320 Gallon Deck Box

Best overall (the only shell bigger than its label)

Sold in 29 sizes and colours on this listing (30–320 gal) — this card is the 320 gal, Rattan Black. Check the size before you add to cart.

Your pick if you want the biggest box in the class and you have checked who is selling it: 75 by 34 inches of resin, a 4.3★/1,182 base, and the one 300-gallon-plus claim on Amazon that fits inside the box's own exterior volume (376 gallons). Not for you if a lid that can blow open in wind is a deal-breaker — that is its tail.

4.3 · 1,182 owner ratingsAmazon · September 2026 · listing-wide base

Pros

• The only 300-gallon-plus box on Amazon whose claimed capacity fits inside its exterior volume — 75 inches long against the 58–68 inch shells sold as '320' to '380'
• The deepest owner base in the class, 4.3★ across 1,182
• Sold in 29 sizes and colours from one listing, so the 320 can be matched to smaller boxes of the same look

Cons

• Sold by a storefront named 'Amzaon'' — a Ningbo e-commerce company trading under a misspelling of Amazon's name; the brand has no website (nunulab.com parks to a lander) and publishes no warranty
• 'Wind blew it open and the plastic snapped all the hinges, pretty cheap brittle plastic' — the seller replaced it; another owner: 'the cover can blow open with strong winds. The piston isn't real strong'
• 'The walls bow out and cause the bottom to come apart' when loaded with cushions; assembly parts 'not all marked', 'wouldn't click' — 122 critical reviews (10% of the base)
• The rating pools 29 variants from a 30-gallon box up; reviews of 33- and 35-gallon units sit on this page

What owners complain aboutDefect reports

The shell is not rigid and the lid is not wind-safe. 'The walls bow out and cause the bottom to come apart'; 'really flimsy at the bottom where the walls are attached'; 'Wind blew it open and the plastic snapped all the hinges'; 'the cover can blow open with strong winds. The piston isn't real strong to hold it shut'. Assembly: 'the parts are not all marked', 'wouldn't click', 'took me 45 minutes'.

10 critical read 2026-09-17 of 122 critical on a 1,182-rating base (10%); flimsy/bowing structure in 4, wind and lid in 2, assembly in 4; dates Sep 2025 → Sep 2026; 10/10 Verified Purchase, 0 Vine; variant lines on the page include 33- and 35-gallon units. · critical reviews read September 2026

Check price at Amazon →

✓ Safety: no active recallCPSC recall API checked 2026-09-16: ProductName=deck box → 0 records, ProductName=NUNU LAB → 0 records, with the positive control ProductName=heater returning 181 records in the same sitting. CPSC's long-standing guidance on storage chests concerns freely falling lids that can trap a child; this box has a lockable lid and a lid that holds itself open. Lock it when small children play nearby, and never let a child climb in.

Why it wins. It is the longest shell in the class by a foot, and the only one whose gallon figure is smaller than its exterior volume. Its base is the deepest here, and the visible cards are all Verified Purchase with no Vine reviews. Set beside boxes that print 370 on a 318-gallon shell, an honest 320 on a 376-gallon exterior is a low bar that only one product clears.

Not for you if: you cannot accept the seller. The offer is sold by “Amzaon’” — a third-party storefront whose seller page names Ningbo Pansen E-commerce Co., trading under a misspelling of the platform’s own name. It ships from the same warehouse and carries the same 30-day return as the others, but it is not Amazon, and the brand behind it has no website. The other catch is in the tail: two owners describe wind lifting the lid, one with every hinge snapped. Site it out of the wind, and lock it.

Double-wall, sold by Amazon: YITAHOME 300 Gallon Double-Wall Deck Box

Buy link pulled (re-read 2026-10-28). The Amazon listing we carded now sells “YITAHOME 60 Gallon Outdoor Storage Box”: 42 × 16.8 × 21.5 inches, 23 pounds, with no 300-gallon size anywhere on it, under the same rating pool. We have not found the 300 on another listing, so the card has no buy button until a listing reads as this box again. What follows is the September 17 read.

On the spec sheet this is the box to buy: double-wall panels, gas struts, a brand with a website, and Amazon.com — not a storefront — as the seller. The owners disagree with the spec sheet. Its histogram is the worst on the page, 8% two-star and 9% one-star, and the critical reviews are about the plastic, not the design: “half of the pieces were broken or cracked” on arrival, “very cheap thin”, and a box that “lasted about a year… ended up warping, especially at the top so now it does not seal”. We carded it because the seller and the construction claim are genuinely different from the rest, and because a reader who values Amazon’s own returns desk should have that option in front of them with its numbers attached.

The metal one: MIRADOR 281 Gallon Aluminum Deck Box

MIRADOR 281 Gallon Aluminum Deck Box (Horizon)

The metal one, from a maker that exists

Showdown Score™

5.6

Good

Good is 5.5 to 6.4.

Likely 3.6 to 7.6

See why it scored 5.6

Low confidence

Low confidence: part of the evidence is unread or thin. The margin is ±2.0, so the true score is likely 3.6 to 7.6.

Owners88 Amazon ratings, read 2.0Failure recordRead from the owner base3.6Hands-on testNo credentialed test yet. A missing test never costs points.None yetTotal5.6

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Sold in 8 sizes and colours on this listing (134–281 gal) — this card is the 281 gal, Latte. Check the size before you add to cart.

Your pick if you would rather pay three times the class price for a box with a manufacturer, a warranty page and wheels: rust-proof aluminum and steel, a soft-close lid, 281 gallons, 4.0★/88. Not for you if you want it built in an afternoon — the tail is bent panels, screw holes that do not line up and a lid hatch owners ruined on the first try.

4.0 · 88 owner ratingsAmazon · September 2026 · early data · listing-wide base

Pros

• A manufacturer, a direct store and a warranty page — the only one of the five with any of the three
• Metal, not snap-together resin: no bowing walls, no bottom pulling away from the sides in the tail
• Wheels on a 120 lb box, and a claimed capacity that sits well inside the shell's 340-gallon exterior

Cons

• 'The sides come bent which makes them difficult to put together (this was not a packaging problem. I bought two and each had both long side panels bent)'; 'the screw holes do not line up'; 'thousands of screws… I still messed up the lid hatch. Once you get it together, they make it impossible to go back' — 17 critical reviews and a 13% one-star share
• 'Both of the lift pistons for the lid' failed on one owner's box; rivet nuts strip if the driver is off vertical
• At $599 it is nearly three times the class price, and 281 gallons is under the 300 mark the rest of this page is sold on; the maker's 370-gallon Urban is $899 direct and not on Amazon
• The rating pools four sizes and two colours; 134- and 175-gallon reviews sit on this page

What owners complain aboutDefect reports

Assembly of a bent metal kit. 'The sides come bent… I bought two and each had both long side panels bent'; 'the screw holes do not line up. Had to leave several screws off'; 'thousands of screws… I still messed up the lid hatch. Once you get it together, they make it impossible to go back'; 'Hold power driver in precisely vertical position… the thread damages so easily… the bolt came out with the rivet nuts'; 'both of the lift pistons for the lid' failed; 'most difficult thing to build I've ever bought from Amazon'.

8 critical read 2026-09-17 of 17 critical on an 88-rating base (19%; histogram 13% one-star); assembly/bent panels/misaligned holes in 6, pistons in 1, delivery in 1; dates Jul 2025 → Apr 2026; 8/8 Verified Purchase, 0 Vine; variant lines include 134- and 175-gallon units. · critical reviews read September 2026

Check price at Amazon →

✓ Safety: no active recallCPSC recall API checked 2026-09-16: ProductName=deck box → 0 records, ProductName=MIRADOR → 0 records, with the positive control ProductName=heater returning 181 records in the same sitting. CPSC's long-standing guidance on storage chests concerns freely falling lids that can trap a child; this box has a lockable lid and a lid that holds itself open. Lock it when small children play nearby, and never let a child climb in.

The only box here from a company: Mirador Outdoor, a Sorara line with a direct store, a dealer program and a warranty page that says “residential use only” and offers an extra year on registration. Aluminum and steel, wheels, a soft-close lid, 120 pounds. It is under the 300 mark and nearly three times the class price, and the maker’s own store sells it for less than Amazon does. Its tail is not the resin tail; it is a metal kit’s tail — “the sides come bent”, “the screw holes do not line up”, “thousands of screws”. If you want bigger from the same maker, the 370-gallon Urban exists, direct-only, at a price above anything on this page — the largest deck box we found from a manufacturer with a name.

SKIP: TARKARI 370 Gallon Deck Box

TARKARI 370 Gallon Deck Box

SKIP

Showdown Score™

6.1

Good

Good is 5.5 to 6.4.

Likely 4.3 to 7.9Was 6.0 in October 2026

See why it scored 6.1

Low confidence

Low confidence: part of the evidence is unread or thin. The margin is ±1.8, so the true score is likely 4.3 to 7.9.

Owners211 Amazon ratings, read 2.5Failure recordRead from the owner base3.6Hands-on testNo credentialed test yet. A missing test never costs points.None yetTotal6.1

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Sold in 14 sizes and colours on this listing (14 variants (sizes and colours; gallon figures not printed in the twister)) — this card is the 370 gal, Black. Check the size before you add to cart.

Your pick if you have decided that the number on the front of a box is measured by someone. TARKARI's '370 gallons' is printed on a shell that is 67.72 by 32.2 by 33.66 inches — 318 gallons of exterior — and that the same seller lists as 320 gallons under the Yardgrace name. 4.3★/211, pooled, and a tail that includes 'it blew apart in a wind storm'.

4.3 · 211 owner ratingsAmazon · September 2026 · listing-wide base

Pros

• Looks like the others — because it is: the same shell four brands sell
• 'Love the size and look' — the first half of a two-star review

Cons

• The claimed 370 gallons is larger than the box's own exterior volume (318 gallons from the listing's dimensions); the same seller, ARTS BOX US, sells the same 67.72 × 32.2 × 33.66 in shell as '320 gallons' under the Yardgrace name
• 'It blew apart in a wind storm. This is a plastic snap together plastic box. If you buy it reinforce the box with wood braces on all corners'
• 'If you put any weight in the bottom of it, the bottom of it sags, and it pulls away from the sides'; 'has already started to bow in the front' after two weeks; 'the sides are bulging' with cushions alone — 31 critical reviews, 15% one- and two-star
• No brand site (tarkari.com parks to a lander), no warranty; the listed weight (30.9 lb) is less than half what the same shell weighs on its sibling listings

What owners complain aboutDefect reports

A snap-together shell that will not stay together. 'It blew apart in a wind storm… reinforce the box with wood braces on all corners'; 'if you put any weight in the bottom of it, the bottom of it sags, and it pulls away from the sides'; 'has already started to bow in the front' after two weeks; 'the sides are bulging' holding cushions alone; 'Bottom and sides kept falling apart' during assembly; 'The bottom just sort of lines up some tabs and slots but nothing clicks in'.

8 critical read 2026-09-17 of 31 critical on a 211-rating base (15%; histogram 7% two-star, 8% one-star); structural bowing/sagging in 5, wind in 1, assembly in 2; dates Jul 2026 → Sep 2026; 8/8 Verified Purchase, 0 Vine; the variant line on the page reads 200 gallons. · critical reviews read September 2026

Check price at Amazon →

✓ Safety: no active recallCPSC recall API checked 2026-09-16: ProductName=deck box → 0 records, ProductName=TARKARI → 0 records, with the positive control ProductName=heater returning 181 records in the same sitting. CPSC's long-standing guidance on storage chests concerns freely falling lids that can trap a child; this box has a lockable lid and a lid that holds itself open. Lock it when small children play nearby, and never let a child climb in.

Stock note, 30 October 2026: Amazon listed the TARKARI 370 Gallon Deck Box as currently unavailable, with no other sellers offering it. We keep it on the page while the listing may restock.

The number on this box is larger than the box. Its listing gives 67.72 × 32.2 × 33.66 inches — 318 gallons if the walls were infinitely thin — and calls it 370. Its seller of record, ARTS BOX US, sells the identical dimensions as “320 Gallon” under the Yardgrace name, and the detail table lists a weight less than half of what the same shell weighs on the sibling listings. The owners’ reports are the class’s, louder: a bottom that “sags, and it pulls away from the sides”, a front that “has already started to bow” in two weeks, and one that “blew apart in a wind storm” with the advice to “reinforce the box with wood braces on all corners”. That is a SKIP on the label alone; the tail makes it an easy one.

The boxes we read and did not card

KAMABOKO 330 (4.3★/570, pooled across 48 variants from 35 gallons): the first shell, sold by KAMABOKO-US; its tail is a lid cracked in the first week and an owner who measured a “150” at 102 gallons. Decksplore 350 (4.4★/149): the first shell under a Portland-based brand with a real website and a “32-climate testing protocol” on its about page — the one badge here with a company behind it, which is why we would read it first at the next audit; its warranty page carries no term. Yardgrace 320 [Upgraded 3.0] (4.2★/127) and Yardgrace 300 (4.6★/83): the same seller as the TARKARI, on both shells; the 300’s own detail table says 270. EFU 380 Gen 2 (4.6★/58 in September; the listing was gone by 28 October): the second shell, part 248A, at 140% of its exterior, three critical reviews in a month including “falls apart very quickly”. KFY 320 (4.4★/198): the second shell’s cousin at 114%, pooled across 35 variants from 30 gallons.

ATMELT 300 (our best-value pick from 17 September): unavailable on Amazon since 27 September, with no seller on its offer list; by 28 October its rating base had fallen from 64 to five. Its shell was the closest to honest of the resin boxes, 294 gallons against a 300 label. It leaves the page; see the re-read above for why nothing replaced it.

We also re-read the credentialed tests. Bob Vila’s month-long trial (page dated 9 August 2026) tops out at the Keter Java 230; The Spruce’s and BHG’s hands-on lists stop there too. None of the three hands-on tests we read puts hands on a 300-gallon box. That is not a gap in our reading; it is the state of the category.

How to pick a 300-gallon deck box

• Divide before you buy. Length × width × height in inches, ÷ 231. If the label is bigger than the answer, the label is fiction. Every listing prints its dimensions; not one prints the arithmetic.
• Read the seller line, not just the brand. Three brands, one seller is common here. “Sold by Amazon.com” is the exception (the YITAHOME 300 when we carded it, and the Decksplore 320 on 28 October), and it is worth something at return time.
• Wind is the enemy of a 68-inch lid. Two of the five boxes we carded in September have tails describing a lid blown open. Site the box against a wall, and use the padlock hole for a lock even if theft is not the worry — it keeps the lid down.
• Bag what you store. No resin box on this page seals; the owners of every box we carded say so. Cushions in bags, chemicals not at all — see our pool-storage page for where chemicals belong.
• If 230 gallons will do, buy the 230. The Keter Luma 230 on our large-deck-box page comes from a company with a warranty document and a decade of owner history. This class exists because people search for it.

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