Drywall calculator — wall and ceiling sheets

Estimate sheets for the inside of one rectangular room: four walls, with an optional ceiling. Enter dimensions in feet, subtract openings in square feet and choose a cutting allowance. The result is an area-based estimate, not a board layout or a specification for fire-rated construction.

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drywall sheet calculator

Room length (ft)Room width (ft)Wall height (ft)Include ceilingTotal door / window openings (ft²)Sheet width (ft)Sheet length (ft)Cutting allowance (%)

Estimated sheets to buy: 17sheets
Net coverage area: 472ft²
Area with cutting allowance: 519.2ft²
Sheet coverage: 32ft² / sheet

Formula

sheets = ceil(([2(L + W)H − openings + ceiling] × [1 + waste/100]) ÷ [sheet width × sheet length])

For walls only, ceiling area is zero. For walls and ceiling, ceiling area is L × W. Round up once, after applying the allowance. The 10% default is an editable planning assumption, not a universal standard. Openings cannot exceed wall area. Small cutouts may not save a sheet; board orientation, joints, offcut reuse and multiple layers change the order quantity.

Worked examples

Input	Result
12 × 10 ft room, 8 ft high; walls only; no openings; 4 × 8 ft sheets; 10% allowance	352 ft² net × 1.10 ÷ 32 = 12.1 → 13 sheets
Same room with ceiling	472 ft² net × 1.10 ÷ 32 = 16.225 → 17 sheets
Same room with ceiling and 40 ft² openings	432 ft² net × 1.10 ÷ 32 = 14.85 → 15 sheets

Drywall sheet sizes and coverage

Sheet dimensions	Coverage per sheet
4 × 8 ft	32 ft² (2.973 m²)
4 × 10 ft	40 ft² (3.716 m²)
4 × 12 ft	48 ft² (4.459 m²)

Sheets for common net areas — 4 × 8 ft, 10% allowance

Area estimates rounded up, before any board-layout check.

Net wall / ceiling area	Estimated sheets
100 ft²	4 sheets
200 ft²	7 sheets
300 ft²	11 sheets
400 ft²	14 sheets
500 ft²	18 sheets
750 ft²	26 sheets
1000 ft²	35 sheets

Questions

How many drywall sheets do I need?

Calculate the wall area as perimeter × height, subtract your chosen openings, add the ceiling if needed, apply a cutting allowance, then divide by sheet area and round up. A 12 × 10 ft room with 8 ft walls and a ceiling needs an estimated 17 sheets of 4 × 8 ft board at 10% allowance, before openings.

Should I subtract doors and windows?

You can subtract their combined area, but small openings do not always reduce the number of whole sheets. For a conservative estimate leave openings at zero, then check a board layout before ordering.

How much waste should I allow?

The default 10% is only a planning assumption. Adjust it for offcut reuse, angled walls, openings and sheet layout. Confirm the quantity with your installer or supplier.

Can I use metric dimensions?

This room estimator uses feet and square feet. Convert lengths with the mm-to-feet tool and opening areas with the m² ↔ ft² converter. A metric 1200 × 2400 mm board is not exactly a 4 × 8 ft board; enter its actual converted dimensions.

Does this include screws, joint compound or multiple board layers?

No. It estimates one layer of sheets only. Fastener spacing, compounds, thickness, fire resistance and moisture requirements depend on the approved assembly and manufacturer guidance.

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