Paint Calculator

How much does 2.5 litres of paint cover?

At the calculator setting of 11 square metres per litre, a 2.5 L tin covers 27.5 square metres with one coat, or 13.75 square metres with two coats, before allowing for waste. These are wall areas, not floor areas: a room with a 14 square metre floor can have far more than 14 square metres of wall.

With the 5% touch-up allowance selected, the two-coat area becomes 2.5 × 11 ÷ 2 ÷ 1.05 = about 13.1 square metres. For a larger area, enter the actual room dimensions above. A 5 L tin covers about 26.2 square metres under the same assumptions. Check the coverage and preparation instructions on your chosen paint; rough or absorbent surfaces reduce the area you can finish.

How many gallons of paint for two coats?

Switch the calculator to imperial to enter feet and read US gallons. The unit switch changes the measurement units and suggested can sizes; it does not change the selected surface or number of coats. For example, 400 square feet of net wall area is about 37.16 square metres. At 11 square metres per litre, two coats and a 5% allowance need about 7.09 litres, or 1.87 US gallons. The suggested order is two US gallons.

A US gallon is about 3.785 litres; an imperial gallon is about 4.546 litres. The gallon results on this site are US gallons. Metric mode suggests 10, 5, 2.5 and 1 L tins; imperial mode suggests 5-gallon, 1-gallon and 1-quart cans. Both start from the unrounded paint requirement. Purchased volume and estimated leftover use the suggested cans in the selected system. Check which sizes your supplier stocks. For the ceiling in a different finish, calculate it separately. Use the primer calculator when the paint instructions call for a separate primer.

How to use the paint calculator

1. Pick Room dimensions and measure length, width and wall height. Measure floor to ceiling, not to the picture rail.
2. Enter the number of doors and windows. The calculator deducts 1.9 m² (20 sq ft) per door and 1.5 m² (16 sq ft) per window, which is accurate for standard openings.
3. Choose a surface preset, or enter Product coverage from your paint label or a measured test. A positive product figure overrides the preset; use 0 to return to it. Match the field’s m²/L or sq ft/US gal unit.
4. Set the number of coats. Two is standard; go to three if you are covering a dark colour with a light one.
5. Read the result: litres or US gallons needed, plus a suggested whole-tin order. The estimate does not compare pack prices or guarantee the cheapest combination.

The formula behind the numbers

Every paint calculation is that one line. The wall area comes from the room perimeter multiplied by the wall height: 2 × (length + width) × height. If you are painting the ceiling too, add length × width.

The spreading rate is printed on the tin, normally as "up to 13 m²/L" or "up to 400 sq ft per gallon". The words up to matter: that figure is measured on a sealed, smooth, non-absorbent test panel. A real wall with filler patches, old wallpaper paste or fresh plaster drinks noticeably more, which is why the surface options here step down from 13 to 5 m²/L.

Worked example

A bedroom 5 m × 4 m with 2.5 m ceilings, one door and one window, two coats of matt emulsion on previously painted walls.

Perimeter = 2 × (5 + 4) = 18 m. Wall area = 18 × 2.5 = 45 m². Deduct 1.9 m² for the door and 1.5 m² for the window, giving 41.6 m². Two coats = 83.2 m² of painting. At 13 m²/L that is 6.4 litres, plus a 5% touch-up allowance = 6.72 litres. The metric suggestion is one 5 L tin and two 1 L tins: 7 L purchased, with 0.6 L beyond the estimated coat coverage, including the allowance.

In US units the same room is 484 sq ft of wall, 448 sq ft after openings, 896 sq ft painted, at 530 sq ft/gal that is about 1.7 gallons, so two gallon tins.

Paint coverage by surface

These ranges and calculator presets are planning assumptions. Enter your exact labelled rate in Product coverage when available; Coverage used in the result confirms the rate applied. For example, 34 m² with two coats at 17 m²/L and a 5% allowance needs 34 × 2 ÷ 17 × 1.05 = 4.2 L. Setting Product coverage back to 0 restores the chosen preset.

How many coats do you really need?

• One coat only works when you are re-coating the same colour in the same finish, with a high-opacity paint.
• Two coats is the calculator default. The selected coating instructions determine the required coat count and coverage.
• Three coats for a strong colour change (dark to light, or any vivid red, yellow or orange, which have weak pigment opacity). A tinted primer usually beats a third top coat on both cost and finish.
• New plaster needs the preparation specified by the coating manufacturer. If a mist coat is specified, use that product’s dilution and coverage instructions and calculate it separately from the finish coats.

Why you should buy slightly too much

Ordering the exact litre figure is a false economy. Tins are sold in fixed sizes, and a second trip for a half-litre top-up risks a different batch: visibly different on a large wall. The 5% allowance covers roller loading, tray residue and the paint left clinging to the tin.

Keep the leftovers sealed and labelled with the room name. Half a litre covers years of scuffs and picture-hook repairs.

Planning your order

Check the inputs before buying: measure the surfaces you need, then apply an allowance and round to whole packs. The guides include worked examples you can follow alongside this calculator.

Painting more than one room? Combine matching paint quantities before choosing tins. The worked example keeps colours and finishes separate and shows how a shared order changes the leftover.