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Free, no sign-up. Works in metric and imperial.
Paint Coverage Estimator
Buying paint is guesswork until you do the math. Enter your total wall length, ceiling height, doors and windows, choose coats and coverage, and this calculator shows your net paintable area plus how many liters or gallons to buy, rounded up with 10% extra for waste.
-Net paintable area
-Paint needed
-With 10% waste
The paint formula
Gross wall area = total wall length x ceiling height. Net paintable area = gross area minus 1.9 m2 per door and 1.4 m2 per window (21 sq ft and 15 sq ft in imperial). Paint needed = round up of (net area / coverage per unit x coats). The calculator then adds 10% waste for spills, roller absorption and touch-ups, and rounds up again to whole liters or gallons.
Worked example
A room with 12 m of walls and a 2.5 m ceiling = 30 m2.
- Minus 1 door (1.9 m2) and 2 windows (2.8 m2): 30 - 1.9 - 2.8 = 25.3 m2 net.
- 2 coats at 10 m2/L: 25.3 / 10 x 2 = 5.06, rounded up = 6 L.
- Plus 10% waste: 6 x 1.1 = 6.6, rounded up = 7 L to buy.
Why add 10% waste
No wall absorbs paint exactly the way the label promises. Spills, roller and brush absorption, cut-in edges, and touch-ups after the furniture goes back all eat into the theoretical number. Buying the extra can up front is cheaper than a second trip mid-project, and leftover paint stored properly keeps for years.
Tips for an accurate estimate
Measure wall length along the baseboards and include alcoves and returns. Use the coverage figure printed on your actual paint can, since matte paints cover less per liter than satin on textured surfaces. If your ceiling is not white or you are painting over a dark color, keep two coats; one coat only works over a similar color in good condition.
Planning estimate only. Results use the list prices shown and may differ from your actual bill. Terms
Frequently asked questions
How many coats should I use?
Two coats is the safe default for most walls: the first coat covers, the second evens out the color and hides roller marks. One coat works only over a similar color in good condition.
What does coverage per unit mean?
It is how much wall area one liter (or one gallon) covers, printed on the paint can. A typical value is 10 m2/L (about 350 sq ft/gal); adjust it to match your paint's label.
Why does the calculator round up?
Paint is sold in whole liters or gallons, so a result like 5.06 liters becomes 6. Rounding up guarantees you do not run out mid-wall, which would leave a visible seam.
How much do doors and windows subtract?
The calculator deducts 1.9 m2 per door and 1.4 m2 per window (21 sq ft and 15 sq ft in imperial), standard average openings. Adjust the counts if your doors or windows are unusually large.