Wall Area Calculator
Paint, wallpaper, drywall and panelling are all bought by wall area — and wall area is not floor area. This calculator computes gross wall area from room dimensions and ceiling height, then deducts standard door and window openings.
Use the net figure for paint and the gross figure for drywall (offcuts around openings become waste anyway).
Enter valid values to see the results.
Formula
Standard deductions: door 1.9 m² (20 ft²), window 1.4 m² (15 ft²). For non-standard openings (patio doors, floor-to-ceiling glazing), measure them and adjust the counts accordingly.
How to measure
- Measure room length and width at floor level and ceiling height at the tallest point.
- Count doors and windows; for oversized openings, count them as 1.5–2 standard ones.
- If walls differ (one wall has three windows), calculate that wall separately: width × height − openings.
Worked example
Practical tips
- For paint, use the net area; for drywall and wallpaper, use gross — cut-outs are waste.
- Textured walls (rough render, brick) take 10–15% more paint than smooth plaster.
- Do not forget the ceiling if you are painting it: ceiling area = floor area.
- Write the net area on the paint can lid — future touch-ups will thank you.
Waste allowance
No waste is added here — material calculators (paint, wallpaper, drywall) apply their own allowances on top of this area.
Standard opening sizes used for deduction
| Opening | Metric | Imperial |
|---|---|---|
| Interior door | 0.9 × 2.1 m = 1.9 m² | 20 ft² |
| Standard window | 1.2 × 1.2 m = 1.4 m² | 15 ft² |
| Patio door (count as 2) | 3.8 m² | 40 ft² |
Common mistakes
- 1 Using floor area to buy paint — wall area is typically 2.3–2.7× the floor area.
- 2 Deducting openings for drywall: the cut pieces are unusable, so sheets should be ordered by gross area.
- 3 Forgetting the ceiling in “wall” calculations when the job includes it.
- 4 Measuring height once — use the largest value, ceilings are rarely level.
Frequently asked questions
How do I calculate wall area of a room?
Add the length and width, multiply by 2, then by ceiling height: 2 × (L + W) × H. A 5 × 4 m room with 2.6 m ceilings has 46.8 m² of walls.
Should I subtract windows and doors?
For paint and wallpaper, yes — deduct about 1.9 m² per door and 1.4 m² per window. For drywall, no: cut-outs become waste, so order by gross area.
How much wall area does a typical room have?
A medium 4 × 4 m bedroom with 2.6 m ceilings has about 41.6 m² gross, roughly 37 m² net after a door and two windows.
How do I measure one wall only?
Width × height of that wall, minus its openings. This is the right approach for feature walls and accent paint.
Does this include the ceiling?
No. Ceiling area equals floor area (length × width) — use the Room Area Calculator and add it if your project includes the ceiling.