Key takeaways
- Shopping by gallons alone. A tall, narrow 120-gallon box and a long, low 120-gallon box hold very different cushions. Length is the spec that matters for bench and chaise pads.
- Using exterior dimensions as interior. The lid lip and 1-inch resin walls eat 2 to 4 inches. A “48-inch” box rarely has more than 45 inches inside.
- Assuming cushions compress. Quality outdoor foam is 1.8 to 2.5 pound density and springs back; you cannot squeeze eight 5-inch cushions into 30 inches of height.
- Forgetting seasonal growth. The set you own now is not the set you will own in three years. Buying one size up costs $30 to $60 more and avoids a second box.
- Ignoring the lid load. If the box will double as a bench, check the seating capacity; most resin boxes are rated for 2 to 3 adults, or 400 to 600 pounds, and cheap ones sag at 250.
- Skipping ventilation. Sealed boxes trap humidity and grow mildew on damp cushions. Look for vents or a slight lid gap, and never store cushions wet.
What's inside
The Short Answer
For a typical four-seat patio set, you need a deck box of at least 100 to 120 gallons (roughly 380 to 450 liters), which translates to an interior of about 48 to 52 inches long, 22 to 26 inches wide, and 22 to 26 inches tall. For a sectional with six or more seat and back cushions, go to 150 to 230 gallons, or about 60 to 72 inches long. The mistake nearly everyone makes is trusting the gallon rating and ignoring the shape: cushions do not compress like pool noodles, and a 48 by 18 by 5 inch bench cushion will not fit in a 46-inch-long box no matter how many gallons it claims. Measure your longest cushion, add 2 inches, and make sure the interior length beats that number before you look at anything else.
Standard Sizes
| Deck box class | Capacity | Exterior L x W x H (inches) | Exterior L x W x H (cm) | Holds | Typical price |
|---|---|---|---|---|---|
| Small | 30 to 50 gal (115 to 190 L) | 30 to 36 x 17 to 20 x 17 to 22 | 76 to 91 x 43 to 51 x 43 to 56 | 2 chair seat pads or 1 bench cushion folded | $40 to $80 |
| Medium | 70 to 90 gal (265 to 340 L) | 44 to 48 x 20 to 22 x 22 to 24 | 112 to 122 x 51 to 56 x 56 to 61 | 4 chair seat pads plus 1 bench cushion, or 2 chaise pads | $70 to $130 |
| Large | 100 to 130 gal (380 to 490 L) | 50 to 56 x 24 to 28 x 24 to 28 | 127 to 142 x 61 to 71 x 61 to 71 | 4 seat plus 4 back cushions from a dining set, or 3 chaise pads | $100 to $200 |
| Extra large | 150 to 180 gal (570 to 680 L) | 58 to 64 x 28 to 30 x 26 to 30 | 147 to 163 x 71 to 76 x 66 to 76 | Full 4-piece conversation set cushions | $150 to $300 |
| Jumbo | 200 to 230 gal (760 to 870 L) | 66 to 72 x 30 to 34 x 28 to 32 | 168 to 183 x 76 to 86 x 71 to 81 | 6-seat sectional cushions plus pillows | $200 to $400 |
| Zippered storage bag | Roughly 170 to 190 gal equivalent | 68 x 30 x 20 | 173 x 76 x 51 | Chaise and sectional cushions; must sit under cover | $20 to $35 |
Interior dimensions are usually 2 to 3 inches smaller than exterior in each direction because of wall thickness and the lid lip. When a listing gives only exterior numbers, subtract 3 inches from length and width and 2 to 4 inches from height to estimate usable space.
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How to Measure Your Space
- Inventory the cushions. Write down every seat pad, back cushion, chaise pad, and throw pillow with its length, width, and thickness. A common bench cushion is 48 by 18 by 3 to 5 inches (122 by 46 by 8 to 13 cm); a dining seat pad is 18 to 20 inches square by 3 to 4 inches; a deep-seat sofa cushion is 24 to 26 by 24 to 26 by 5 to 6 inches.
- Find the longest single piece. This sets your minimum interior length. Add 2 inches for the lid lip and easy removal. A 48-inch bench cushion therefore needs a 50-inch interior, which usually means a 52 to 54 inch exterior.
- Stack by thickness. Total the thickness of everything you plan to stack in one pile. Four 4-inch seat pads plus four 5-inch back cushions is 36 inches, so you either need a 36-inch-tall interior (rare) or two side-by-side stacks in a box at least 40 inches wide, or a longer box that holds two stacks end to end.
- Calculate volume with a 20 percent buffer. Multiply each cushion’s length, width, and thickness in inches, add them together, divide by 231 to get gallons, then multiply by 1.2. Cushions do not nest perfectly and you will want room for a cover or a cushion bag.
- Measure the spot on the deck. Allow the box footprint plus 4 inches at the back for the lid to swing open against a wall or railing, and 24 inches in front to stand while loading.
- Check the path. Boxes ship flat but assembled boxes are 2 to 6 feet long; make sure you can get one through the gate or up the stairs to where it will live.
By Room or Use Case
Balcony or small deck with two chairs
Two 20-inch seat pads and two back cushions total about 12 to 15 gallons, so a 30 to 50 gallon box is more than enough and doubles as a seat. Look for 30 to 36 inches long so a rolled outdoor throw or a folded 48-inch bench cushion fits diagonally.
Four-seat dining set
Four seat pads at 20 by 20 by 4 inches and four backs at 20 by 18 by 4 inches come to about 25 to 30 gallons of foam, but their square shape wastes space. A 70 to 90 gallon medium box with a 44 to 48 inch interior holds them in two stacks with room for a tablecloth and umbrella cover.
Bench and porch swing cushions
Bench cushions are the ones that trip people up because of length. A 48-inch cushion needs a 50-inch interior; a 60-inch porch swing cushion needs 62 inches, which pushes you into extra-large or jumbo boxes even though the volume is small. If you refuse to buy a 72-inch box for one cushion, choose a bench cushion in two 24-inch halves or store it in a zippered bag under a covered porch.
Conversation set or loveseat group
A four-piece set (loveseat, two chairs, table) typically has 4 deep seat cushions at 24 by 24 by 5 and 4 backs at 24 by 18 by 5, roughly 45 to 55 gallons of foam. With the 20 percent buffer and pillows, a 100 to 130 gallon large box fits it all in two stacks.
Sectional and chaise lounges
Six seat and six back cushions at 26 inches deep add up to 80 to 100 gallons before pillows. This is jumbo territory: 200 to 230 gallons, 66 to 72 inches long, 30 inches or more wide. Chaise pads are 72 to 78 inches long and do not fit in any consumer deck box flat; fold them in half (only if the foam is hinged or under 3 inches thick) or use a 68-inch zippered bag.
Common Sizing Mistakes
- Shopping by gallons alone. A tall, narrow 120-gallon box and a long, low 120-gallon box hold very different cushions. Length is the spec that matters for bench and chaise pads.
- Using exterior dimensions as interior. The lid lip and 1-inch resin walls eat 2 to 4 inches. A “48-inch” box rarely has more than 45 inches inside.
- Assuming cushions compress. Quality outdoor foam is 1.8 to 2.5 pound density and springs back; you cannot squeeze eight 5-inch cushions into 30 inches of height.
- Forgetting seasonal growth. The set you own now is not the set you will own in three years. Buying one size up costs $30 to $60 more and avoids a second box.
- Ignoring the lid load. If the box will double as a bench, check the seating capacity; most resin boxes are rated for 2 to 3 adults, or 400 to 600 pounds, and cheap ones sag at 250.
- Skipping ventilation. Sealed boxes trap humidity and grow mildew on damp cushions. Look for vents or a slight lid gap, and never store cushions wet.
FAQ
How many gallons do I need for a standard four-piece patio set?
Plan on 100 to 130 gallons (380 to 490 liters). The cushions themselves are about 50 gallons of foam, but their shapes waste space and you want room for pillows and covers. A medium 70 to 90 gallon box works only if the cushions are thin, 3 inches or less.
Will a 48-inch bench cushion fit in a 48-inch deck box?
No. The exterior measurement includes walls and the lid lip, so interior length is usually 45 to 46 inches. You need a box with an exterior length of at least 52 inches, or an interior length listed at 50 inches or more.
Is a zippered cushion bag a good substitute for a deck box?
Only under cover. A 68 by 30 by 20 inch bag at $20 to $35 holds as much as a 170-gallon box and stores flat when empty, but it is water-resistant rather than waterproof and offers no protection from rodents or from being crushed. On an open deck, use the bag inside a box or shed.
Which deck box size is the best all-round buy for 2026?
For most homes, a 120 to 150 gallon box, 54 to 60 inches long, covers a dining set or conversation set with room to spare, works as a two-person bench, and costs $120 to $220. It is the size least likely to be outgrown when you add a chaise or a second set of cushions.
