Paint Coverage Calculator
Coverage is the spread rate read the other way round: not how much paint a room takes, but how much wall one tin finishes once the coats are counted. Set the spread rate from your tin, pick the tin size and the coats, and the top line is the area that tin covers, with the area per gallon or per litre beside it. Enter your walls as well and the same page still tells you the volume and the number of tins.
- Wall area
- not yet
- Openings
- 0 sq ft
- Coats
- Spread rate, editable
- Per
- sq ft per gallon
- Tin size
- Units
- Leading with
Measure each wall along the floor and up to the ceiling and type the two numbers. A ceiling is one more surface: its length and its width. The spread rate opens on 350 sq ft per gallon, which is the figure commonly printed on interior emulsion tins, and the one on your tin is the one that counts, so change it.
Walls and ceilings
Each surface is a width and a height, in feet.
- not yet
Doors and windows
Anything you are not painting comes off here. Add one line per size and say how many of it there are.
Worked examples
Each one is run through the same two functions as your own numbers. Load one to see it in the fields.
Common questions
- What is paint coverage, or spread rate?
- It is the area a fixed amount of paint covers in one coat: square feet per US gallon, or square metres per litre. Tins print it because it is the only number that turns a room into a shopping list. Interior emulsion is commonly printed at about 350 square feet per gallon, or about 11 square metres per litre, which is where the field on this page opens, and your tin's own figure replaces it.
- How much wall does one tin cover?
- The tin size times the spread rate, divided by the coats. A one-gallon tin at 350 square feet per gallon covers 350 square feet in one coat and 175 square feet in two. A 2.5 litre tin at 11 square metres per litre covers 27.5 square metres in one coat and 13.75 in two. The top line does that arithmetic for whatever spread rate, tin size and coat count you set.
- Why does a second coat halve the coverage?
- Because the same wall gets painted twice. The spread rate describes one coat over one pass, so two coats over a wall use twice the paint and a tin therefore reaches half as far. This page divides by the coats rather than hiding the assumption, which is why the coverage figure moves the moment you change the coat control.
- Why does my tin state a different figure?
- Spread rate varies with the paint, the sheen and what it is going onto. A bare or freshly plastered wall drinks more than a previously painted one, a textured surface has more area than its measurements suggest, and a heavy colour change needs more paint on the surface. The printed figure is for that paint under the maker's stated conditions, and it is the one to type in here.
- Can I still work out how much to buy?
- Yes. Add your walls and any doors and windows and the line under the coverage figure gives the net area, the volume it takes and the number of tins to buy, rounded up to whole tins. Switching the page to lead with the paint needed instead is one control away, and everything you typed stays put.
- Is anything uploaded?
- No. The arithmetic runs in your browser and nothing is sent anywhere. Your settings are kept in your own browser storage so the page reopens as you left it.
Exact arithmetic on the area, coats and spread rate you give, with your openings subtracted. The spread rate on your tin is the one that counts. It cannot know how porous the wall is or how much colour change you are covering.