Paint Calculator
Work out how much paint you need for the walls of a room, minus doors and windows, plus the ceiling if you paint it too.
Paint needed
8.36 litres
Area to paint
41.8 m²
Please note: The result is an estimate and has been rounded. Actual costs and values may differ, and no rights can be derived from this calculation.
How this number is calculated
The blocks use your input. Change a value above and they update with it.
Step 1 · Wall area
Step 2 · Ceiling
Step 3 · Doors and windows
Step 4 · Area to paint
Step 5 · Paint in litres
Step 6 · Paint needed
How the calculation works
Work out how much paint you need to paint a room. Enter the room size, the number of doors and windows, how many coats you apply and the coverage of your paint.
First the calculator works out the wall area: the perimeter of the room (twice the length plus the width) times the height. If you paint the ceiling too, length times width is added. Doors and windows are taken off: 2 m² (21.5 sq ft) per door and 1.5 m² (16.1 sq ft) per window. That area times the number of coats, divided by the coverage, is the amount of paint.
Formula
Area to paint = 2 × (length + width) × height + ceiling (length × width) − 21.5 sq ft per door − 16.1 sq ft per window. Paint = area × coats ÷ coverage (area per gallon or litre).
Assumptions
- The room is rectangular and all walls are the same height.
- A door counts as 2 m² (21.5 sq ft) and a window as 1.5 m² (16.1 sq ft). If your windows are much larger or smaller, adjust the count.
- The coverage applies to a smooth, primed wall. A rough or porous surface takes more paint.
- Skirting boards, trim and frames are not counted separately.
Example calculations
The button fills in the calculator above, so you can carry on from there.
-
Room, walls only
Paint needed
8.36 litres
Room length 5 m · Room width 4 m · Wall height 2.6 m · Doors 1 · Windows 2 · No · Number of coats 2 · Coverage 10 m²/L · litres · m²
-
Room with ceiling
Paint needed
12.36 litres
Room length 5 m · Room width 4 m · Wall height 2.6 m · Doors 1 · Windows 2 · Yes · Number of coats 2 · Coverage 10 m²/L · litres · m²
-
Large living room
Paint needed
13.6 litres
Room length 8 m · Room width 5 m · Wall height 3 m · Doors 2 · Windows 4 · No · Number of coats 2 · Coverage 10 m²/L · litres · m²
Frequently asked questions
How much paint do I need for a room?
For a room of 12 by 10 feet with 8-foot walls, one door and two windows, there are 298 square feet of wall. With 2 coats and paint that covers 350 sq ft per gallon, that is 1.70 US gallons, so you would buy 2 gallons.
How many coats of paint do I need?
Usually 2. Over the same or a similar colour, 1 coat is sometimes enough. Going from dark to light, or on new or porous walls, you may need a primer or a third coat.
Should I buy extra paint?
A small margin helps, especially on rough or porous walls and for touch-ups later. Paint comes in fixed sizes, such as quarts and gallons in the US or 1, 2.5 and 5 litre tins in the UK: round up to what the shop sells.
What coverage should I enter?
The coverage is on the tin or the product sheet. Interior wall paint in the US often covers 350 to 400 sq ft per gallon; in the UK and Europe 10 to 12 m² per litre is common. The calculator converts between the two.
Why 21.5 sq ft per door and 16.1 sq ft per window?
These are generous averages for a door with its frame and a window of ordinary size. For a precise result, measure your windows and doors and count them as one or more units of these sizes.
Sources and checks
Sources
How we check it
This calculator has 10 fixed checks: 5 calculations with a result that is fixed in advance, and 5 cases of invalid input that must be rejected. They all run automatically every time we publish; if one fails, the calculator does not go live.
See the calculations
- Room length 5 m · Room width 4 m · Wall height 2.6 m · Doors 1 · Windows 2 · No · Number of coats 2 · Coverage 10 m²/L · litres · m² → Paint needed 8.36 litres
- Room length 5 m · Room width 4 m · Wall height 2.6 m · Doors 1 · Windows 2 · Yes · Number of coats 2 · Coverage 10 m²/L · litres · m² → Paint needed 12.36 litres
- Room length 3.5 m · Room width 3 m · Wall height 2.5 m · Doors 1 · Windows 1 · No · Number of coats 1 · Coverage 8 m²/L · litres · m² → Paint needed 3.63 litres
- Room length 12 ft · Room width 10 ft · Wall height 8 ft · Doors 1 · Windows 2 · No · Number of coats 2 · Coverage 350 ft²/US gal · gallons · ft² → Paint needed 1.7 gal
- Room length 8 m · Room width 5 m · Wall height 3 m · Doors 2 · Windows 4 · No · Number of coats 2 · Coverage 10 m²/L · litres · m² → Paint needed 13.6 litres
Changes
- : First version. Sources added and content reviewed.
Last reviewed: · How we build and check our calculators
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