Plywood Calculator
This plywood calculator works out how many sheets a floor, wall or roof needs, with the sheet layout counted properly, so full sheets and rips are separate numbers.
Sheets by Area
Sheet Layout
Counts how the sheet grid actually falls across the space, full sheets and rips separately.
Plywood Cost
How to use the Plywood Calculator
If you just need a number to order, use Area, area divided by sheet size plus waste.
If you want to know what the job will actually look like, use Layout. It works out how the 4 ft sheet grid falls across the space and reports full sheets and rips separately, because a 30 ft width takes seven full sheets and a 2 ft rip, and that rip is a different problem from a percentage.
Plywood Cost adds fasteners to the sheet count and lets you price the longer sheets side by side. A 4 by 10 costs more each, but it can work out cheaper per square foot and leaves fewer joints to stagger.
Plywood formula
sheets = ceiling(area ÷ sheet area × (1 + waste%))courses = ceiling(width ÷ sheet width)sheets per course = ceiling(length ÷ sheet length)
Counting by area gives the order quantity. Counting by layout gives the truth about offcuts, and the two rarely agree exactly.
| Sheet | Area | Sheets per 1,000 sq ft |
|---|---|---|
| 4 × 8 ft | 32 sq ft | 32 |
| 4 × 9 ft | 36 sq ft | 28 |
| 4 × 10 ft | 40 sq ft | 25 |
| 4 × 12 ft | 48 sq ft | 21 |
Worked example
A 40 × 30 ft floor in 4 × 8 sheets:
- Area: 1,200 sq ft
- By area: 1,200 ÷ 32 = 37.5, plus 10% = 41.25 → 42 sheets
- By layout: 30 ÷ 4 = 7.5 courses → 7 full courses and one 2 ft rip; 40 ÷ 8 = 5 sheets per course
- That is 35 full sheets plus 5 ripped sheets = 40 sheets
The layout count is lower because the 2 ft offcut from each ripped sheet is reusable on the same row. The area method does not know that.
What the result means
Sheets are indivisible, so the grid matters more than the percentage. A width that lands on a 4 ft multiple wastes almost nothing; one that lands at 4 ft 1 in wastes most of an extra course.
Leave the expansion gap. An eighth of an inch between sheets on subfloor and sheathing. Sheets butted tight buckle when they take up moisture, and the resulting ridge telegraphs through flooring.
Stagger the joints. Sheets should break on different framing members row to row, which uses a few more part sheets and makes the assembly far stiffer.
Common mistakes
- Ordering exactly what the area maths says. Sheets come whole, and a damaged corner ruins one.
- Butting sheets tight. They swell. Gap them an eighth.
- Running all joints on one line. Stagger them, it is what makes a sheathed wall or floor act as a diaphragm.
- Ordering sheets before checking the framing. Every sheet edge has to land on a stud or a joist, so the stud spacing decides where the joints can fall, not the other way round.
- Forgetting the sheets are heavy. A 4 × 8 of ¾ in plywood is about 70 lb. That is a two-person lift up a stair, every sheet.
- Assuming plywood and OSB are interchangeable. They differ in weight, edge swell and how they take moisture, though the sheet count is the same.
Frequently asked questions
How many sheets of plywood do I need for 1200 square feet?
Thirty-eight 4 by 8 sheets to cover the bare area, or about 42 with ten percent waste. Laid out as a real grid on a 40 by 30 foot floor it comes to 40 sheets, 35 full and 5 ripped down for the last course.
How many square feet is a sheet of plywood?
A standard 4 by 8 sheet is 32 square feet. Longer sheets are 36, 40 and 48 square feet for 9, 10 and 12 foot lengths, which are common for wall sheathing on taller walls.
Should I leave a gap between plywood sheets?
Yes, about an eighth of an inch on subfloor and sheathing. Panels absorb moisture and expand, and sheets butted tight will buckle at the joint. Many tongue and groove subfloor panels have the gap built into the profile.
How much does a sheet of plywood weigh?
A 4 by 8 sheet of half inch plywood is roughly 40 pounds and three quarter inch around 70. OSB of the same thickness runs a little heavier. It matters for planning the lift more than for the material list.
How do I calculate sheets for a wall or roof?
The same way as a floor, but use the sloped roof area rather than the footprint. Work out the roof area from the pitch first, then divide by the sheet size. Walls use the gross wall area less large openings.
Is OSB or plywood better for subfloor?
Both meet code and the sheet count is identical. Plywood dries faster and holds fasteners slightly better at the edges; OSB is cheaper and more uniform but swells at cut edges if it gets wet and stays wet. Keep either one dry during the build.
Sources and assumptions
Sheet sizes are the standard North American 4 ft widths at 8, 9, 10 and 12 ft lengths. Nominal thickness and actual thickness differ slightly on sanded panels.
The layout count assumes sheets run their long dimension along the length and that offcuts from a ripped course are reusable within that course. Complex plans, openings and staggered joints will differ.
Expansion gap of ⅛ in follows APA panel installation guidance for sheathing and subfloor.
Panel grade, thickness and span rating are governed by code and by the framing spacing, this tool counts sheets, it does not specify them.
Sheet layout, edge support and the expansion gap follow APA panel guidance; the gap is not optional, and it is the mistake that shows up as a ridged floor a year later.