How to Measure a Room for Paint (And Calculate Exactly How Much You Need)
Wall area minus doors and windows, multiplied by coats, divided by coverage rate. Get the number that tells you exactly how many tins to buy, and never buy too few.
Buying paint is where DIY budgets blow. Either you buy way too much (waste), or you run out mid-job (second trip, color matching issues). The math is simple: wall area × coats ÷ coverage. The hard part is getting the wall area right, which is where most people fail. Your iPhone solves that in 90 seconds.
Por que medir isto
- Avoid buying excess paint that goes to waste
- Avoid running out mid-job and re-mixing colors
- Get accurate per-room cost for budgeting
- Compare paint brand pricing on a like-for-like basis
O que você precisa
- iPhone with Ruler AR (LiDAR optional but speeds it up)
- Room Scan (LiDAR) or Manual Room Builder
- Material Calculator in the app
Passo a passo
- Measure the room outline. Open Ruler AR → Room Scan (LiDAR) or Manual Room Builder (any iPhone). Walk the perimeter; the app builds the floor plan automatically. Save as a project named "Room, Paint".
- Ceiling height. Use Height mode. Tap floor to ceiling. Most rooms 240-260 cm. Older houses 280-300 cm. New builds often 240 cm exactly.
- Subtract doors and windows. In the saved project, the app already detected doors and windows (LiDAR) or you added them in the manual editor. Each one is excluded from paintable area automatically.
- Wall area calculation. Wall area = floor perimeter × ceiling height − sum of door areas − sum of window areas. Tap Material Calculator in the project → Paint. The app calculates it.
- Set coats and coverage. Most paints state coverage in m²/L on the tin. Default is 10 m²/L per coat. Two coats is standard for fresh painting; three for going from dark to light. Adjust in the Material Calculator.
Dicas
- Always add 5-10% for touch-ups and small mistakes
- Ceiling and walls use different paint (ceiling is matt to hide imperfections; walls are washable matte/eggshell)
- Buy from one production batch, color can vary slightly between batches
Erros comuns
- Measuring just the floor area, paint covers walls, not floors
- Forgetting to subtract doors and windows (saves 5-15% of total paint)
- Using single-coat coverage when two coats are needed, always read the tin
Perguntas frequentes
How many litres of paint per coat per 10 m²?
Roughly 1 litre per 10 m² for one coat on a smooth wall. Textured surfaces (stipple, stucco) use 30-50% more.
Do I need two coats?
Almost always yes. One coat looks streaky and shows brush marks. Exceptions: going from one shade of white to a similar white might work in one coat.
How much does ceiling paint cover?
Same as wall paint (10 m²/L typical). Ceiling area equals floor area for flat ceilings. Vaulted or sloped ceilings: use the actual surface area.