Paint Calculator
How many gallons to paint a room — doors and windows subtracted.
Wall Preview
1 door · 2 windowsThese are example numbers. Tap any field below and enter your own measurements — every result updates instantly as you type.
Enter the room dimensions — the length, width and ceiling height — then set the number of coats, doors and windows.
Optional — material cost per gallon of paint.
Estimate
Live Material Cost
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Coverage varies with surface texture and color change; one gallon typically covers 350–400 sq ft per coat.
How the paint calculator works
BuildCalc's paint calculator turns three measurements — the room length, width and ceiling height — into a gallon count. It multiplies the wall perimeter by the height to get the gross wall area, subtracts a flat allowance for every door and window, then multiplies the net wall by your coat count.
That paintable surface is divided by the per-gallon coverage — 350 to 400 square feet for one coat of interior paint — and rounded up to whole gallons, because paint is sold by the can. Coverage drops on rough or porous walls and when a big color change needs an extra coat, so treat the result as a solid starting point and confirm against the label on your paint.
Guides
- How much paint for a 10×10 room? — 320 sq ft of wall in 2 coats, with the openings subtracted.
- How much paint for a 12×12 room? — math, a room-size table and the variables that change the number.
Paint calculator FAQ
How much paint do I need for a room?+
Measure the room length, width and ceiling height. Multiply the perimeter — two times length plus width — by the height to get the wall area, subtract the doors and windows, then divide by the coverage of a gallon and multiply by the number of coats. BuildCalc does this for you and rounds up to whole gallons.
How many square feet does a gallon of paint cover?+
A gallon of interior wall paint covers about 350 to 400 square feet in one coat on a smooth, primed surface. Rough or porous walls absorb more and pull that figure toward 300, so BuildCalc lets you pick 350 or 400 to match your wall.
How many coats of paint should I use?+
Two coats is the standard for a durable, even finish, and it is what most manufacturers assume in their coverage ratings. A single coat can work when you are repainting the same color over a sound surface; expect three coats when going from a dark color to a light one.
Should I subtract doors and windows from the paint estimate?+
Yes — they are surfaces you will not roll. BuildCalc subtracts a flat 21 square feet for each door and 15 square feet for each window, which keeps the gallon count from running high on a room with several openings.
How much paint do I need for a 12x12 room?+
A 12 by 12 foot room with an 8 foot ceiling has about 384 square feet of wall. After subtracting one door and two windows, two coats need a little under 2 gallons at 350 square feet per gallon — so plan on 2 gallons. Enter your exact openings above for a precise figure.
Should I buy extra paint for touch-ups?+
It is worth keeping a small amount in reserve. Because BuildCalc rounds up to whole gallons, you will usually have some left over already — store it sealed and labeled so a future scuff or nail hole is an easy fix instead of a new shopping trip.