Paint Calculator
Work out how much paint a room needs from its dimensions, number of coats, doors, and windows — with the ceiling, primer, and total cost included.
كيفية استخدام هذه الحاسبة
- 1Measure the room's length, width, and ceiling height in feet.
- 2Enter the number of doors and windows so their area is deducted.
- 3Choose the number of coats — two is standard for a colour change.
- 4Check the coverage figure on your paint can and enter it, since it varies a lot by product.
طريقة الحساب
Paint quantity formula
wall area = 2 × (length + width) × ceiling height paintable = wall area − (doors × 21) − (windows × 15) + ceiling gallons = paintable × coats ÷ coverage per gallon
The perimeter of the room multiplied by the ceiling height gives the total wall surface. Standard openings are deducted at 21 square feet per door and 15 per window. Multiplying by the number of coats and dividing by the coverage printed on the can gives the volume needed — always rounded up, since you cannot buy two-thirds of a can.
مثال محلول
A 14 ft × 12 ft room with 9 ft ceilings has 468 sq ft of wall. Deducting one door and two windows leaves 417 sq ft. Two coats at 350 sq ft per gallon needs 2.4 gallons — so three one-gallon cans, or a 5-gallon bucket with some left over.
Paint Calculator: الدليل الكامل
Why one coat is almost never enough
Manufacturers quote coverage for a single coat on a smooth, primed, similarly-coloured surface. Real rooms rarely qualify. Two coats is the working default: the first evens out absorption and the second delivers the actual colour and sheen.
Going from a dark colour to a light one can need three coats, or two coats over a tinted primer — which is cheaper and faster than a third topcoat. Deep, saturated colours such as strong reds and yellows are the worst offenders because their pigments have poor hiding power.
What actually changes coverage
Surface texture is the biggest factor. Smooth drywall is the best case at 350–400 sq ft per gallon. Light orange-peel texture drops that to around 300, heavy knockdown to 250, and bare masonry or stucco can halve it. Every square foot of texture is more surface area than the flat measurement suggests.
Porosity matters just as much. New drywall, patched areas, and bare wood drink the first coat, which is exactly what primer is for — it seals the surface so the topcoat sits on it rather than soaking in.
Application method has a smaller but real effect. Spraying is fast but wastes paint in overspray; rolling is the most efficient use of the can. Cutting in with a brush is neither, but it is unavoidable at edges.
Buying: cans, buckets, and one extra
Paint is sold in quarts, gallons, and five-gallon buckets, and the per-gallon price drops sharply at the bucket. If the estimate lands above about four gallons, price the bucket — it is usually cheaper and guarantees every wall comes from a single tint batch.
Tint batches vary slightly between mixes, exactly like tile dye lots. If you need more than one can of a custom colour, boxing them — pouring all the cans into one larger container and stirring — eliminates any visible difference between walls.
Keep the leftover, labelled with the room and the colour code. Touch-ups a year later are trivial with the original paint and nearly impossible without it.
الأسئلة الشائعة
How much paint do I need for a 12x12 room?
A 12 ft × 12 ft room with 8 ft ceilings has 384 sq ft of wall before deductions. After one door and one window, two coats at 350 sq ft per gallon needs about 2.1 gallons — so three one-gallon cans. Enter your actual ceiling height above, since it changes the answer substantially.
Do I need primer?
Yes for bare drywall, bare wood, patched areas, stains, or a dramatic colour change. No for a repaint in a similar colour over sound, clean, previously painted walls. Tinted primer under a deep colour often saves a full topcoat.
How much paint for the ceiling?
Ceiling area is simply length × width. Switch the ceiling option above to include it in the total. Flat ceiling paint typically covers a little further than wall paint because ceilings are usually smooth and already primed.
Should I deduct doors and windows?
For a normal room, yes — this calculator uses 21 sq ft per door and 15 per window. If your openings are unusually large, such as sliding patio doors or a picture window, measure them and adjust the count so the deducted total matches the real area.