Paint Coverage Calculator
Open toolEstimate how much paint you need for a room based on wall area and coverage rate.
Estimate how much paint you need for the walls of a room from the total wall length, wall height, the area of doors and windows you will not paint, the number of coats, and the coverage rate printed on the paint tin.
How it works
Wall area = Total wall length × Wall height. Paintable area = Wall area − Doors & windows area (never below zero). Paint needed = Paintable area × Number of coats ÷ Coverage rate.
The tool has no built-in units: use feet with square feet per gallon, or metres with square metres per litre, and keep them consistent. The Paint needed figure comes out in the volume unit of your coverage rate (gallons or litres) and is shown without a unit label.
How to use it
- Measure the total wall length: for a rectangular room, add up the four walls, which is 2 × (length + width).
- Enter the Wall height.
- Enter the combined area of any doors and windows to exclude (0 if you prefer to ignore them).
- Enter the Number of coats and the Coverage rate from the tin.
- Read Paint needed, and round up to the next full can.
Options & controls
Inputs
- Total wall length (perimeter)
- The combined length of all the walls to paint, in feet or metres. Must be greater than 0. Default: 140.
- Wall height
- Floor-to-ceiling height in the same unit. Must be greater than 0. Default: 8.
- Doors & windows area to subtract
- The area of openings that will not be painted, in square feet or square metres. Optional; empty counts as 0. Default: 0.
- Number of coats
- How many coats you plan to apply. Must be greater than 0. Default: 2.
- Coverage rate
- How much area one unit of paint covers, from the tin — for example 350 sq ft per gallon, or 10 m² per litre. Must be greater than 0. Default: 350.
- Reset
- In the title row. Restores the five sample values.
Reading the results
Results
- Paintable area
- The wall area left after removing doors and windows, in square units.
- Paint needed
- The amount of paint for all the coats, in gallons or litres depending on the unit of your coverage rate.
- Copy
- Copies both figures as text.
- Assumptions & notes
- A reminder that the amount is an estimate. On phones it sits behind a toggle.
Tips & guidelines
- A typical interior door is about 20 sq ft (1.9 m²) and a typical window about 15 sq ft (1.4 m²). Skipping the subtraction gives a cautious over-estimate.
- Check the coverage rate on the tin. It varies by brand, colour and product type. Dark colours, new plaster, and porous or rough surfaces use more paint.
- Buy a bit more than the estimate — 5–10% is common — and always round up to whole cans. It is far better to have leftover paint for touch-ups than to run short mid-wall and risk a colour mismatch from a different batch.
- If you are also painting ceilings, trim, or using a primer, work out those areas separately and add them.
Limits
- Only wall area is calculated: ceilings, trim, skirting boards, and radiators are not included.
- It does not convert units, so mixing feet with litres will give a wrong answer.
- It gives the total amount, not can sizes or the number of cans to buy.
Saved in your browser
Nothing. Values return to the defaults when you refresh.