Plywood sheet calculator
This divides the area you enter by one sheet and rounds up — a buying estimate, not a cutting plan. It does not lay the sheets out, stagger the joints or subtract openings, so for a tight or complex area sketch the layout too and confirm the count before you load up.
Enter the size of the area, how many areas of that size, and the sheet you are using; the tool totals the area, divides by a sheet, adds waste and rounds up to whole sheets. That rounded figure is the number to buy.
Exemple détaillé
A 20 ft × 20 ft floor is 400 square feet. In 4×8 sheets at 32 ft² each that is 400 ÷ 32 = 12.5 sheets before waste. Add 10% and round up and you are buying 14 sheets. Switch to 4×4 panels and the same floor takes 25 before waste, 28 after.
In metric: a 6 m × 6 m floor is 36 m². A 1220 × 2440 mm sheet covers 2.98 m², so 36 ÷ 2.98 = 12.1 sheets before waste; add 10% (13.3) and round up — 14 sheets.
Sur le chantier
A subfloor, checked by rows. 24 ft × 36 ft is 864 ft², ÷ 32 = 27 sheets, 29.7 → 30 with 10%. Now lay it out: the 8 ft side runs along the 36 ft, so a row is 4½ sheets, and 24 ft across at 4 ft a sheet is 6 rows. 6 × 4½ = 27 — and the half-sheet that ends one row starts the next, which staggers the joints for free. Twenty-seven exactly, so 30 is three spares for the one that gets rained on and the two with a bad edge. When the row count and the area count agree, order.
Sheathing a 9 ft wall. 120 ft of perimeter × 9 ft = 1,080 ft². In 4 × 8s stood up that is 30 sheets a course plus a 1 ft strip along the top — thirty rips and thirty extra joints. Buy 4 × 9 sheets (36 ft²): 1,080 ÷ 36 = 30, no rips, and the waste is only the gable triangles. Do not take the windows out of sheathing; the sheet goes on whole and the opening is cut from inside.
A roof deck from the pitch. A 34 × 44 footprint (overhangs in) at 6/12 is 1,496 × 1.118 = 1,672 ft² of roof — the pitch tool gives the multiplier. ÷ 32 = 52.3, × 1.1 = 57.5, so 58 sheets. Use the footprint alone and you are six sheets short with the felt already cut.
What went wrong?
Quick referencefor sheet goods
- Sheet areas
- 4 × 8 = 32 ft² · 4 × 9 = 36 · 4 × 10 = 40 · 4 × 4 = 16
- Sheets per 100 ft², 10% waste
- 4 × 8: 3,4 → 4 · 4 × 9: 3,1 → 4
- Roof area
- footprint (overhangs in) × pitch multiplier — 4/12: 1.054 · 6/12: 1.118 · 8/12: 1.202
- Wall area
- perimeter × height, openings left in
- T&G subfloor
- the tongue is not coverage — a 4 × 8 T&G nets about 31.5 ft²
- Metric sheet
- 1,220 × 2,440 mm = 2.98 m² · per 10 m² with 10% waste: 3.7 → 4 sheets
Waste & overagewhat to add, and why
- Sheathing crews carry 10% on a rectangular floor or wall and 15–20% on a cut-up roof with hips, valleys and dormers — every angled cut throws away a triangle. The waste field starts at 10%.
- Sheets sell by the lift in fixed counts; if the buy line is a few sheets under a lift, ask the yard about the price break.
Mistakes to catchbefore you order
- Sheeting a roof off the footprint area — the roof surface is longer by the pitch multiplier, so use the rafter-length page's area or multiply first.
- Typing the wall height without the rim and plates; sheathing usually runs from the sill to the top plate.
- Counting a gable end as a rectangle; it is a triangle plus a rectangle, and the tool wants the true area.
What an inspector looks forthe building inspector, at sheathing and again at the floor
On this part of the job
- The panel's grade stamp — thickness, span rating, exposure class and the face orientation are all printed on the sheet, and the stamp is the evidence.
- Panel layout: joints staggered, the long dimension running the way the drawing shows, and every edge supported where support is required.
- The nailing pattern at panel edges and in the field, and that the fasteners have not been over-driven through the face. This is counted on shear walls.
- The gap left between sheets, which the panel manufacturer specifies for expansion.
- Blocking at unsupported edges where the detail or the shear-wall schedule calls for it.
Have this ready
- One offcut with the grade stamp readable, kept aside.
- The nailing schedule from the drawing.
- The panel manufacturer's installation sheet for spacing and fastening.
Every figure an inspector measures against comes from the code your jurisdiction has adopted, the stamped drawing, or the manufacturer's printed instructions — so none of them are printed here. Look the number up in your own book, type it into the tool, and the arithmetic is yours.
La formule
sheets = (total area × (1 + waste)) ÷ sheet area, rounded up
Total area is length times width times the number of areas. Dividing by one sheet's area gives a fractional count; the waste factor covers the offcuts and rounding up turns it into whole panels you can actually buy.
Questions
- How many sheets of plywood do I need?
- Total the area you are covering, divide by the area of one sheet, add a little for waste and round up to whole sheets. A 4×8 sheet covers 32 square feet, so 400 square feet of subfloor is 400 ÷ 32 = 12.5 sheets, about 14 once you allow for cuts. This tool does the division and the rounding.
- What size is a sheet of plywood?
- The common panel is 4 feet by 8 feet, which is where this tool starts, and 4×4 half-sheets are sold too. Metric panels are usually quoted around 1.22 by 2.44 metres, the same panel in the other units. Pick the size in the tool and the count follows.
- How much waste should I allow for sheathing?
- Ten percent is a reasonable default. A big open floor or roof with full sheets going down wastes little; a cut-up area with lots of openings, hips or short runs wastes more, so raise the factor for those. The offcuts often fill in small areas, which the waste allowance covers.
- Do I need to match the sheet direction?
- For a straight area count, no — the tool works from total area and sheet area, not the layout. If the direction of the face grain or the stagger of the joints matters for strength or looks, plan the sheet layout on paper as well; the count here still tells you roughly how many to buy.
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