AnyTool
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How much paint do I need to paint a room?

Work out the wall area, subtract the doors and windows, multiply by the number of coats and divide by the paint’s coverage. AnyTool Paint Calculator does this live: enter a room’s length, width and height (wall area = perimeter × height, with an optional ceiling) or a wall area you already measured, set how many doors and windows to deduct, choose your coats and coverage, and it shows the net paintable area, the litres or gallons of paint needed, and the number of cans to buy — rounded up to your can size — plus an optional cost. Typical coverage is about 10 m² per litre or 350 sq ft per US gallon per coat, but it varies, so buy roughly 10% extra. Everything is computed in your browser.

  • Paint = (net area × coats) ÷ coverage; net area = walls (+ ceiling) − openings
  • Wall area = 2 × (length + width) × height; or enter the area directly
  • Deducts doors and windows by count × area (typical sizes pre-filled)
  • Rounds up to whole cans of your can size; optional price gives a budget
  • 100% in your browser — no upload, no signup, works offline

What is

Paint quantity (paint coverage)

The amount of paint a job needs, found by dividing the net paintable area — total wall area (optionally plus the ceiling) minus the doors and windows you will not paint — multiplied by the number of coats, by the paint’s coverage rate. Coverage is the area one unit of paint covers in a single coat, typically around 10 square metres per litre or 350 square feet per US gallon for a smooth, sealed surface; porous, bare or textured surfaces and big colour changes need more. The result is rounded up to whole cans because paint is sold in fixed sizes.

Calculators

Related terms

Paint coverageSquare metres per litreNumber of coatsWall areaPrimerSpreading rate

Frequently Asked Questions

Wall area = 2 × (length + width) × height; subtract doors and windows, multiply by coats, then divide by coverage. A 4×3 m room 2.5 m high is about 35 m² of wall — minus ~4 m² of openings, × 2 coats ÷ 10 m²/L ≈ 6.2 litres.

First find the wall area: add the room’s length and width, double it for the perimeter, and multiply by the ceiling height. For a 4 m × 3 m room 2.5 m high that is 2 × (4 + 3) × 2.5 = 35 m². Subtract the openings you will not paint — say one door (~1.9 m²) and two windows (~1.1 m² each), about 4.1 m² — to get roughly 30.9 m² net. Multiply by the number of coats (two is usual for a colour change) and divide by the paint’s coverage, around 10 m² per litre: 30.9 × 2 ÷ 10 ≈ 6.2 litres. AnyTool Paint Calculator does this live and rounds up to whole cans of the size you buy.

About 10–12 m² per litre, or roughly 350–400 sq ft per US gallon, for one coat on a smooth, sealed wall — less on porous, bare or textured surfaces.

As a rule of thumb, one litre of quality wall paint covers about 10–12 square metres in a single coat, and one US gallon covers roughly 350–400 square feet — many calculators use 350 sq ft per gallon as a conservative default. These figures assume a smooth, previously painted and sealed surface; a porous, bare, freshly plastered or textured wall soaks up far more, and the first coat always absorbs more than the second. Always check the spreading rate printed on your paint tin and use that in the calculator, since it varies by paint type and brand.

Yes — you do not paint glass or doors, so deduct them. A standard door is about 1.9 m² (21 sq ft) and a window about 1.1 m² (12 sq ft).

Deducting openings stops you over-buying paint for surfaces you will never roll. A standard interior door is roughly 1.9 m² (about 21 sq ft) and an average window around 1.1 m² (about 12 sq ft), though you should adjust for larger patio doors or picture windows. AnyTool Paint Calculator lets you enter the number of doors and windows and the area of each — pre-filled with typical sizes — and subtracts them from the gross wall area before working out the paint. For a tidier finish you can still leave a little extra to cut in around frames.

Usually two coats. One coat may do over a similar colour, but a big colour change, bare or patchy surfaces, or dark-to-light usually needs two coats plus sometimes a primer.

Two coats is the safe default for an even, durable finish, and it is what AnyTool uses. A single coat can be enough when you are repainting a similar colour on a sound, sealed surface. But a major colour change — especially going from dark to light, or covering a strong or stained colour — often needs two full coats and sometimes a separate primer or undercoat, which is paint the basic estimate does not add. Bare, repaired or very porous surfaces also drink the first coat, so factor in a primer and buy about 10% extra paint for touch-ups.

Detailed Explanation

Methodology

How the Paint Calculator Works

The calculator finds the net paintable area, then converts it to paint. From room dimensions the wall area is the perimeter times the height — 2 × (length + width) × height — with the ceiling (length × width) added optionally; alternatively you enter a wall area you measured. It then subtracts the openings you will not paint (doors and windows, each as count × area), multiplies the remaining net area by the number of coats, and divides by the paint’s coverage to get the volume. That volume is rounded up to whole cans of the size you buy, and an optional price per litre or gallon yields a cost. It works in metric (m, m², litres, m²/L) or imperial (ft, ft², US gallons, ft²/gal).

  • Paint = (net area × coats) ÷ coverage
  • Wall area = 2 × (length + width) × height; ceiling = length × width
  • Net area = gross area − Σ(openings count × area)
  • Cans = ceil(volume ÷ can size); cost = volume × price
  • All math is client-side JavaScript with no server round-trip
How It Works

Coverage, Coats and Typical Figures

Coverage (or spreading rate) is the area one unit of paint covers in a single coat. As a working default, one litre covers about 10–12 m² and one US gallon about 350–400 sq ft on a smooth, sealed wall; many calculators use 350 sq ft per gallon to stay safe. Two coats is the usual default for an even finish and any colour change, while one coat can suffice over a similar colour. Porous, bare, freshly plastered or textured surfaces absorb noticeably more, and a dark-to-light change may need an extra coat or a separate primer that the basic estimate does not include.

  • ~10–12 m² per litre · ~350–400 sq ft per US gallon, per coat
  • Two coats is the default for colour changes; one over a like colour
  • Standard door ≈ 1.9 m² (21 sq ft); window ≈ 1.1 m² (12 sq ft)
  • First coat absorbs more than the second
  • Use the spreading rate printed on your own paint tin
Limitations

Why Real Paint Usage Varies

The estimate assumes the coverage you entered holds across the whole job, but real usage swings with the surface and method. Porous, bare or textured walls drink far more than a smooth, sealed one; a major colour change — especially dark to light — often needs an extra coat or a primer the basic figure omits; and rollers and sprayers waste more than a brush. Paint type and brand also change the spreading rate. Because of this the result is a shopping estimate, and buying roughly 10% extra covers second coats, touch-ups and future repairs.

  • Assumes one steady coverage across the whole job
  • Bare, porous or textured surfaces use much more paint
  • Dark-to-light changes may need an extra coat or primer
  • Application method (brush vs roller vs spray) changes waste
  • An estimator for shopping — buy ~10% extra for touch-ups
Privacy & Security

Privacy and Offline Use

All computation runs in the browser, so the room sizes, openings and prices you enter are never sent to a server, there is no account or tracking, and the page works offline after first load. The calculator is built on a shared, unit-tested paint engine so its behaviour is consistent and verifiable across metric and imperial, and the full result — net area, paint needed, cans to buy and any cost — can be copied to the clipboard with one tap.

Paint estimation: in-browser (AnyTool) vs typical online paint calculators
CapabilityAnyToolTypical online paint calculators
ProcessingRuns in your browserOften server-side
Input modeRoom dimensions or wall areaUsually dimensions only
UnitsMetric and imperialOften one system
OpeningsDoors & windows deductedSometimes
CeilingOptionalRarely
Coats & coverageBoth editableOften fixed
Cans to buyRounded to can sizeSometimes
Optional costPer litre or gallonRarely
Works offlineYes (PWA)No
Cost / signupFree, no signupOften ad-heavy or gated

AnyTool computes the paint estimate locally and uploads nothing. Comparison as of June 2026.