How to Calculate Drywall
Learn how to estimate drywall sheets for simple rectangular walls.
Start with wall area
For a simple rectangular room, calculate the four-wall area as 2 × (length + width) × wall height. Subtract major openings such as doors and windows when they are large enough to materially change the estimate.
Convert area to sheets
Multiply the sheet length by its width to find the coverage of one sheet. Divide the required wall area by that sheet area and round up. Add a project-appropriate allowance for offcuts and damage.
Worked example
A 5 m × 4 m room with 2.4 m walls has 43.2 m² of gross wall area. Subtracting 6 m² of openings gives 37.2 m². A 2.4 m × 1.2 m sheet covers 2.88 m². With 10% allowance, the planning area is 40.92 m², or about 15 sheets.
Related tool
Measure each wall and opening
For a simple rectangular room, the gross wall area is 2 × (length + width) × wall height. Measure each wall if the room is irregular or has different ceiling heights. Subtract large doors and windows where doing so materially improves the estimate, but remember that offcuts around openings may still be usable elsewhere depending on the layout.
Worked example
A room is 4 m long, 3 m wide and 2.4 m high. The gross wall area is 2 × (4 + 3) × 2.4 = 33.6 m². If a door and windows together occupy 3.0 m², the net area is about 30.6 m². A sheet measuring 1.2 m × 2.4 m covers 2.88 m² nominally, so 30.6 ÷ 2.88 = 10.625 sheets. Round up to 11 sheets before allowing for cuts and layout waste. The final order depends on sheet orientation, room shape and the manufacturer's guidance.
Allow for layout and board type
Sheet dimensions, thickness and edge profile vary. Wet areas, ceilings, fire-rated walls and other special applications may require a specific board type and installation system. Do not choose a product solely because it has enough square-metre coverage. Check local building requirements and manufacturer instructions for the intended use.
Common mistakes to avoid
- Forgetting to measure wall height or assuming every wall has the same height.
- Mixing metres and centimetres in one calculation.
- Rounding down a partial sheet instead of rounding up.
- Assuming every offcut can be reused, especially around openings or corners.
- Ignoring separate materials such as joint compound, tape, screws and corner bead.
Use the Drywall Calculator for a planning estimate, and confirm board selection and installation details with the product documentation or a qualified installer.