Home & Garden

Paint Calculator

Enter room dimensions, doors, windows, coats, and coverage to estimate wall area, paintable area after deductions, paint required with waste, whole units to buy, and cost. Works in feet/gallons or metres/litres. An estimate — coverage varies by surface and paint.

Last updated: September 30, 2026

Your result · Buy (rounded up)

2gal

Whole units including waste.

Paintable area: 301sq ft
Exact paint needed: 1.89gal
Estimated cost: $90.00

Wall area: 352sq ft
Deducted openings: 51sq ft

Free · No signup · Math stays in your browser

What your result means

Buy is the headline: whole gallons or litres to purchase, waste included. Exact paint needed shows the unrounded figure underneath.

Paintable area is walls (plus ceiling if included) minus door and window openings — the surface your coats must cover.

How the calculation works

Measure walls (plus ceiling if ticked) and subtract standard door and window openings.
Multiply by coats and divide by the tin’s coverage rate, then add the waste percentage.
Round up to whole units — that is what you buy — and multiply by price for cost.

Formula

paintable = walls (+ ceiling) − openings; paint = paintable × coats ÷ coverage (+ waste); buy whole units

Wall area2 × (length + width) × height (+ ceiling if included)
Deductionsdoors × 21 + windows × 15 (sq ft standards)
Paint requiredpaintable × coats ÷ coverage × (1 + waste)
To buyround exact paint UP to whole gallons/litres

Worked examples

Example: 12×10 ft room, 8 ft walls, 2 coats at 350 sq ft/gal
roomUnit: ftlength: 12width: 10height: 8doors: 1windows: 2ceiling: falsecoats: 2coverage: 350wastePct: 10price: 45
Result: Wall area 352 · Deducted openings 51 · Paintable area 301 · Exact paint needed 1.89 · Buy (rounded up) 2 · Estimated cost $90.00
Example: 4×3 m room, 2.4 m walls, 1 coat at 32 sq m/L
roomUnit: mlength: 4width: 3height: 2.4doors: 1windows: 1ceiling: falsecoats: 1coverage: 32wastePct: 10price: 0
Result: Wall area 33.6 · Deducted openings 3.3 · Paintable area 30.3 · Exact paint needed 1.04 · Buy (rounded up) 2 · Estimated cost $0.00

Assumptions

What this calculation takes for granted — check these before relying on the result.

Assumptions:

Default values are an example 12×10 ft room — replace with your measurements.
Openings use standard deductions (door 21 sq ft / 1.95 sq m, window 15 sq ft / 1.4 sq m). Measure large openings for precision.
Coverage is per coat on a prepared, primed surface at the stated spread rate.
Buy quantity always rounds up — paint is sold in whole units.

Limitations

Why your real figure may differ:

Coverage is not universal: porous plaster, dark-to-light colour changes, and textured walls drink far more paint than the tin rate.
Unprimed drywall, stains, and repairs need primer or extra coats this page does not add.
Brushes, rollers, tape, primer, and ceilings painted separately are excluded unless entered.

Frequently asked questions

What does coverage per unit mean?

The area one unit of paint covers in one coat on a prepared surface — e.g. 350 sq ft per gallon or 32 sq m per litre. Rough or porous surfaces achieve less; check the tin and adjust down for thirsty walls.

How much extra is waste percentage?

It reserves paint for roller absorption, spills, cut-in overlap, and touch-ups. 10% suits straightforward rooms; textured or repaired walls deserve 15–20%.

Should the ceiling be included?

Only if you are painting it the same colour and coverage. Ceilings often need a dedicated flat paint — tick the box only when the same tin covers it.

Why buy more than the exact figure?

Paint sells in whole units and running short mid-wall leaves visible lap marks between batches. The rounded-up figure includes waste precisely to avoid a second trip.

New

Home & Garden