Plywood Calculator

A standard plywood sheet is 4 ft by 8 ft, which covers 32 sq ft. Common thicknesses run from 1/4 inch to 1 inch, with 1/2, 5/8, and 3/4 inch the most common.

A plywood calculator divides the area you need to cover by 32 sq ft, the face area of one 4 ft by 8 ft sheet, and rounds up to whole sheets. A 24 ft by 20 ft floor is 480 sq ft, which is exactly 15 sheets. At $45 per sheet that is $675.

The formula in plain words

Find the area of the floor, wall, or roof deck. A sheet covers 32 sq ft, so divide the area by 32. If the answer has a decimal, round up, because you cannot buy part of a sheet.

The waste box adds 10% to the area first, then divides and rounds up. It covers the offcuts that end up too small to use.

Worked examples

Example 1, the default: 24 ft by 20 ft, $45 per sheet.

• Area: 24 × 20 = 480 sq ft
• Sheets: 480 ÷ 32 = 15 exactly
• Cost: 15 × $45 = $675
• With 10% waste: 528 ÷ 32 = 16.5, rounded up to 17 sheets, or $765

Example 2, a small shed floor: 12 ft by 10 ft.

• Area: 12 × 10 = 120 sq ft
• Sheets: 120 ÷ 32 = 3.75, rounded up to 4, or $180
• With 10% waste: 132 ÷ 32 = 4.125, rounded up to 5 sheets, or $225

The waste setting added a whole sheet here because 4.125 only barely passes 4. That is the right call, since you would be short by a few inches otherwise.

Sheets by area

Area	Sheets	With 10% waste
120 sq ft	4	5
192 sq ft	6	7
400 sq ft	13	14
480 sq ft	15	17
1,200 sq ft	38	42

How to measure

Measure each floor, wall, or roof section separately and add the areas. For walls, multiply length by height and subtract large openings only if they are bigger than a full sheet, since small window cutouts still use most of a sheet.

Think about the layout as well as the area. A 24 ft wall of 8 ft sheets takes 3 across with no cutting. A 10 ft wall takes one full sheet and a 2 ft piece, and the leftover 6 ft piece may not be useful elsewhere.

Common mistakes

• Ordering by area alone on a room with an odd shape. Each cut piece can end up a partial sheet.
• Mixing thickness on one deck. Sheets of different thickness leave a ridge at the seam.
• Forgetting that subfloor sheets are laid with the long edge across the joists, with ends staggered. Staggering changes the cutting pattern.
• Ignoring the panel’s span rating. Rating, thickness, and joist spacing must match, and your local code decides.
• Leaving out the expansion gap that panel makers call for between sheets.

Laying sheets with no waste

Take the 24 × 20 ft floor. Sheets run 8 ft along the 24 ft side, so each row is 3 sheets, and 20 ft across is 5 rows of 4 ft, which is 15 sheets with no cutting.

Seams should not line up from row to row. Start every second row with a half sheet, 4 ft long. Cut a sheet in half, use one half to start the row, and the other half finishes the far end of the same row. Nothing is wasted. Leave the gap the panel maker specifies between sheets, and put panel edges over framing.

Sheet count for walls and roofs

For a wall, multiply its length by its height. An 8 ft ceiling and a 40 ft wall is 320 sq ft, which is exactly 10 sheets, with window openings cut out of those sheets. A roof deck uses the sloped area, not the footprint, so convert it with the pitch multiplier from the roof area calculator first. A 1,000 sq ft footprint at 6/12 becomes 1,118 sq ft and needs 35 sheets before waste.

Related calculators

For the OSB alternative, use the OSB calculator. The joist spacing calculator helps lay out the framing underneath, and the decking board calculator covers an exterior deck surface. For wall framing, see the stud calculator. Structural sizing should be confirmed with a licensed professional.