Plywood Calculator

sheets = ceil( area × ( 1 + wastage ÷ 100 ) ÷ sheet area ) required area = area × ( 1 + wastage ÷ 100 ) purchased area = sheets × sheet area

area

Area to cover in square feet — a floor outline for subfloor sheathing, a sloped plane for a roof, or a wall face with the openings already taken off

sheet area

Area of one sheet: 32 sq ft for a 4x8 sheet, 40 for 4x10 and 48 for 4x12

wastage

Cutting allowance as a percentage — the default 10% covers staggered joints on a floor and trimming at a rake, and a 0 is legal only when whole sheets really do fit

sheets

Sheets to buy, rounded up once at the end of the chain rather than at every step

purchased area

Area of the sheets you actually buy, which is always at or above the required area — the gap is what the rounding up costs you

Measure the surface first and decide what counts as area: on a floor it is the outline of the room, on a roof it is the sloped plane rather than the plan footprint, and on a wall it is the face with the openings subtracted. Then pick the sheet size you can actually handle — a 4x12 sheet is 48 sq ft and also 40 kg, and two people cannot carry one up a ladder. Set the allowance from what the job does to the sheets, not from habit: a straight subfloor with the room dimensioned to a multiple of 4 ft can run at 5%, a roof with hips and valleys wants 15%, and a wall full of windows is closer to 15% than to 10%. The last figure is the one to look at before you pay: the purchased area is what the yard loads onto your truck, and subtracting the required area from it tells you exactly what the rounding up cost.

1. An 800 sq ft floor in 4x8 sheets, 10% allowance

   1. Area with waste: 800 × 1.10 = 880 sq ft
   2. One 4x8 sheet: 4 × 8 = 32 sq ft
   3. Sheets: 880 ÷ 32 = 27.5, rounded up to 28
   4. Purchased area: 28 × 32 = 896 sq ft, against the 880 the job needs
   5. The same required area in metric: 880 sq ft = 81.8 sq m

   The defaults, and the rounded-up half sheet is the number worth noticing: 27.5 sheets means the 28th one is there to be cut, and what is left over is 16 sq ft rather than a whole sheet. The sheet count is what you order, the required area is what you tell the supplier, and the purchased area is what arrives — read them as three steps of the same sentence rather than as three answers.

2. A 480 sq ft roof plane in 4x12 sheets, 5% allowance

   1. Area with waste: 480 × 1.05 = 504 sq ft
   2. One 4x12 sheet: 4 × 12 = 48 sq ft
   3. Sheets: 504 ÷ 48 = 10.5, rounded up to 11
   4. Purchased area: 11 × 48 = 528 sq ft, against the 504 the job needs
   5. The same required area in metric: 504 sq ft = 46.8 sq m

   Bigger sheets mean fewer of them: 504 ÷ 48 is 10.5 sheets against 15.75 for the same area in 4x8, and the difference is most of why roofers order the long ones. It is also why this example has to be read next to the weight — a 4x12 sheet is around 40 kg, so the saving is real and so is the handling problem. The rounding is deliberately at the end: cutting 10.5 up to 11 before applying the allowance would turn this into 12 sheets.

3. A 32 sq ft platform in 4x8 sheets, no allowance

   1. Area with waste: 32 × 1.00 = 32 sq ft
   2. One sheet is 32 sq ft, so 32 ÷ 32 = 1 exactly
   3. Rounded up: still 1 sheet, and the purchased area equals the required area

   An allowance of zero is a legal input and the other two fields are not — a zero area has nothing to cover, while a zero allowance is a real decision you can make when whole sheets fit: a single 4x8 platform, a sheet laid in a frame that was built to the sheet. Note that the rounding is invisible here: an exact whole number of sheets must not become two, which is why the count rounds with a tolerance rather than with a bare ceiling.

This page counts sheets and does not lay them out. It does not know how your sheets divide into the room, so it cannot tell you whether the last row needs a rip cut down its length — a 10 ft wide floor with 4 ft sheets is 2.5 sheets across however you arrange them, and that half sheet is what the allowance is for. It does not subtract openings for you, so measure a wall as the face minus doors and windows before entering it, and it has no opinion on thickness, grade, span rating or whether the surface needs tongue and groove. It also counts one surface: a floor with a subfloor and an underlayment is two runs of this page, and a roof is two planes. Nails, glue, screws and the panel clips some engineered floors want are not counted at all.

How many sheets of plywood do I need for 800 square feet?

28 sheets of 4x8 at a 10% cutting allowance, which covers 896 sq ft of board for an 880 sq ft requirement. The same floor in 4x12 sheets is 19 sheets, because each one covers 48 sq ft instead of 32 — fewer pieces to handle, and each piece about 40 kg.

How much area does a sheet of 4x8 plywood cover?

32 sq ft, and the other two sizes on this page are 40 sq ft for a 4x10 and 48 sq ft for a 4x12. Note that the sheet is a nominal 4 ft by 8 ft before surfacing: the actual panel is 1219 by 2439 mm, which is a fraction of a millimetre under the imperial size and makes no difference to a count.

What cutting allowance should I use for plywood waste?

10% is a good default and it is where this page starts, because plywood always gets cut: floor sheets are staggered so the joints do not line up, roof sheets are trimmed at the rake and the ridge, and wall sheets go around every opening. Drop it to 5% when the surface is dimensioned to the sheet, and raise it toward 15% for a roof with hips and valleys or a wall with a lot of openings. Zero is only right when whole sheets genuinely fit.

Is the waste the same as for drywall?

No, and that is the whole difference between the two pages. Drywall goes on in whole sheets and gets cut mainly at the ends of a wall, so a lower allowance is normal; plywood is cut for staggered joints, rake edges and openings. Same arithmetic, different allowance — and the sheet sizes on this page are the same 4x8, 4x10 and 4x12 that the drywall page uses.

Do I subtract windows and doors from a wall?

Yes, and the page does not do it for you. Measure the wall face, then subtract the area of each opening before entering it, because a sheet cut around a window leaves offcuts that are usually too small to use elsewhere. Count the opening at its rough size rather than the window size — the frame takes more of the sheet than the glass does.

Why does the area come out in square feet when I entered square metres?

Because the display unit of an output is fixed and does not follow the unit you typed in. Enter 100 sq m and the page reports the requirement as 1,184 sq ft and 110.0 sq m, so the metric figure is there next to it; the sheet count is unaffected either way. Read the pair rather than converting by hand.

• Plywood — panel sizes, thicknesses and the grading stamps a sheet carries — Wikipedia
• Approximate Conversions from U.S. Customary Measures to Metric — the square feet and square metres compared on this page — National Institute of Standards and Technology