Plywood Calculator — Sheets for Floors, Walls and Roofs
Works for subfloors, wall sheathing and roof decking. Enter the area, pick the sheet size, and it allows for the waste each job actually produces.
Take this list to the store
We'll email the quantities above, what you typed in, and a link that reopens this calculator already filled in — so you can adjust it on your phone in the aisle.
How to work it out
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Measure the area to cover
Floor area for a subfloor. Wall area for sheathing. For a roof, use the roof shingles calculator first to convert the footprint to true sloped area, then bring that figure here.
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Pick the sheet size
4 × 8 ft is standard and fits any vehicle. Longer sheets mean fewer seams, which matters most on a subfloor — every seam is a potential squeak — but they need a truck and two people.
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Add waste for the cuts
Ten per cent on a plain rectangular floor. Fifteen on a roof with hips and valleys, or a wall with many window and door openings, because each one turns a full sheet into an cut-off.
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Plan the layout before cutting
Seams have to land on a joist, stud or rafter, and rows should be staggered so four corners never meet. Sketching the layout on paper first usually saves a sheet, and always saves the sheet you cut wrong.
Sheets by area
Including 10% waste.
| Area | 4 × 8 sheets | 4 × 10 sheets | 4 × 12 sheets |
|---|---|---|---|
| 100 sq ft | 4 | 3 | 3 |
| 200 sq ft | 7 | 6 | 5 |
| 300 sq ft | 11 | 9 | 7 |
| 500 sq ft | 18 | 14 | 12 |
| 800 sq ft | 28 | 23 | 19 |
| 1000 sq ft | 35 | 28 | 23 |
| 1500 sq ft | 52 | 42 | 35 |
| 2000 sq ft | 69 | 55 | 46 |
A 4 × 8 sheet covers 32 sq ft. Divide your area by 32 and add waste for a quick check.
Thickness by job
| Job | Thickness | Support spacing | Note |
|---|---|---|---|
| Subfloor | 3/4 in. T&G | 16 in. joists | Glue and screw. 19/32 only at 16 in. or less. |
| Subfloor, 24 in. joists | 1-1/8 in. or 3/4 T&G | 24 in. | Check the span rating stamp. |
| Wall sheathing | 7/16 in. OSB | 16 in. studs | The usual for exterior walls. |
| Roof decking | 5/8 in. | 24 in. rafters | 1/2 in. only at 16 in. spacing. |
| Shed floor | 3/4 in. | 16 in. | Use exterior grade, not interior ply. |
The span rating stamped on every sheet is the figure that matters. It overrides any table, including this one.
How many sheets of plywood for 1,000 square feet?
A thousand square feet plus 10% waste is 1,100 sq ft. In 4 × 8 sheets at 32 sq ft each that is 35 sheets. In 4 × 12 sheets, 23.
For a subfloor the longer sheets are worth considering — fewer seams means fewer places for a squeak to develop later.
Read the span rating, not the thickness
Every structural sheet carries a stamp with two numbers, like 32/16. The first is the maximum rafter spacing it can span as roof decking; the second is the maximum joist spacing as subfloor, both in inches.
That stamp is what the building inspector looks at. Thickness alone does not tell you whether a sheet is rated for your spacing.
Glue the subfloor, always
Construction adhesive on every joist before the sheet goes down, then screws rather than nails. The glue is what stops squeaks — a screwed-but-unglued floor develops them within a couple of years as the wood dries and moves.
It adds maybe twenty minutes and a few tubes of adhesive to the whole job.
Leave the expansion gap
An eighth of an inch between sheets, everywhere. Sheet goods swell when they take up moisture, and sheets butted tight have nowhere to go — they buckle upwards at the seam, which telegraphs through whatever flooring goes on top.
Most tongue-and-groove subfloor is designed with the gap built into the joint. On square-edged sheets you have to leave it yourself.
Plan the layout and you will buy fewer sheets
The sheet count above assumes ordinary waste. A ten-minute sketch usually beats it.
Take a 12 × 14 ft room. Laid one way, 4 ft sheets across a 12 ft dimension gives three full-width rows with no rip at all — 12 divides by 4 exactly. Laid the other way, across 14 ft, you get three rows plus a 2 ft strip, and that strip has to be ripped from full sheets you then cannot use elsewhere.
Same room, same area, and the second layout costs you two or three sheets. Before ordering, check whether either dimension divides cleanly by 4 — and if one does, run the sheets that way.
Three more rules worth following: stagger the end joints between rows like brickwork, never let four corners meet at a point, and start alternate rows with a half sheet so the pattern breaks naturally.
How many sheets for a shed floor?
A 10 × 12 ft shed floor is 120 sq ft. With 10% waste that is 132 sq ft, so 5 sheets of 4 × 8.
Use 3/4 in. exterior-grade or pressure-treated ply, not interior. A shed floor sits close to the ground, takes condensation from underneath, and interior ply delaminates within a couple of wet seasons.
Run the sheets across the joists, glue and screw them down, and leave a small gap at the walls so the floor can move without pushing the frame apart.
How this is worked out
No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.
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area = length × width, summed over every sectionRooms or wall panels total together. -
× (1 + waste ÷ 100)10% plain, 15% with many openings or a cut-up roof. -
÷ sheet area, rounded upA 4 × 8 sheet is 32 sq ft, 4 × 10 is 40, 4 × 12 is 48. -
fixings = sheets × 50Roughly one every 6 in. at edges and 12 in. in the field.
Common questions
How many square feet in a sheet of plywood?
Thirty-two for a standard 4 × 8 ft sheet. A 4 × 10 is 40 sq ft and a 4 × 12 is 48.
How thick should a subfloor be?
3/4 in. tongue and groove over joists at 16 in. centers. At 24 in. centers you need 1-1/8 in. or a sheet specifically rated for that span — check the stamp.
What is a span rating?
The two numbers stamped on every structural sheet, like 32/16. The first is the maximum rafter spacing for roof use, the second the maximum joist spacing for floor use, in inches. It matters more than the thickness.
Plywood or OSB?
OSB is cheaper and structurally equivalent for sheathing and most subfloors. Plywood handles getting wet better and dries faster, which is why many builders still prefer it for floors and anywhere exposure is likely during the build.
Do I need to glue the subfloor?
Yes. Construction adhesive on every joist, then screws. It is the single thing that stops a floor squeaking, and it costs a few tubes of adhesive.
How much gap between sheets?
An eighth of an inch. Sheets swell with moisture and butted-tight seams buckle upwards, which shows through any flooring laid over them.
How many screws per sheet?
About 50 — roughly every 6 in. around the edges and every 12 in. through the middle. Fifty sheets needs about 2,500, so buy by the box.
Can I use interior plywood for a shed floor?
No. Interior grade delaminates once it gets damp, and a shed floor always gets damp. Use exterior grade or pressure-treated ply.
Where these figures come from
Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.
- APA – The Engineered Wood Association — span ratings, panel grades and fastening schedules
- International Residential Code R503 — subfloor thickness against joist spacing
- Manufacturer panel stamps — the span rating printed on every structural sheet
Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 11, 2026.