Paint Calculator
How much paint a room needs.
| Wall area (before deductions) | 416 sq ft(2 × (length + width) × height) |
| Doors & windows deducted | 60 sq ft(3 × about 20 sq ft each) |
| Paintable wall area | 356 sq ft |
| Area to cover with 2 coats | 712 sq ft |
| Paint needed | 2 gal(at 350 sq ft per gallon) |
| Buy | 3 gal(round up — you cannot buy a part tin) |
| In litres | 7.7 L |
Results update instantly and are computed entirely in your browser. For general information and planning only — not engineering, structural or code advice.
About the paint calculator
Paint is sold by volume but its job is to cover area, so the whole calculation is about turning a room into square feet of paintable surface. The starting point is the wall area: twice the sum of the room's length and width, multiplied by the ceiling height. Add the ceiling if you are painting it, and subtract openings, because a door or a window is about twenty square feet of wall you do not have to cover. Coverage per gallon is the number that decides the answer, and it is printed on the tin. Most interior paints cover between 350 and 400 square feet per gallon on a smooth, sealed wall for a single coat, but that figure falls sharply on rough, porous or unpainted surfaces, which drink the first coat. If you are painting bare plaster or fresh drywall, assume less coverage and expect to need a primer. Coats are the other variable people underestimate. One coat rarely gives an even finish unless you are refreshing the same colour; a colour change usually needs two, and a dramatic change, or covering a dark colour with a light one, sometimes three. Multiply the wall area by the number of coats before dividing by coverage, or you will buy half the paint you need. This calculator gives the paintable area, the total area including coats and the number of gallons, rounded up because paint is sold in whole containers. Keep a little left over for touch-ups. It assumes standard openings and a fixed coverage figure — measure your own walls rather than trusting a nominal room size, and check the coverage claim on the tin you actually buy.
This calculator returns estimates for planning and general information only. It is not engineering, architectural, structural, electrical or code advice, and it cannot replace a qualified professional who has seen the site. Material quantities depend on the actual dimensions, the product you buy and local building codes, so confirm the figures before ordering materials or starting work, and always follow local regulations.
Common questions
How many coats should I allow for?
Two for most rooms, and often three when the colour is a big change or the surface has never been painted. The calculator treats coats as a multiplier on the wall area, so changing from two to three raises the quantity by fifty percent — which is exactly why running out near the end is so common when only one coat was planned.
What coverage figure should I enter?
Use the number printed on the tin rather than a guess. Typical emulsion claims around 350 square feet per gallon, but primers, exterior paints and textured products vary widely, and a porous or bare surface absorbs appreciably more than the stated figure. If in doubt, enter a slightly lower coverage so you order up rather than short.
Should I subtract doors and windows?
Yes, but roughly. The calculator deducts a standard allowance for each opening you count, which is accurate enough over a whole room. Leave one opening in the count if you would rather have a little spare paint, since leftover paint is the cheapest insurance against a mid-wall touch-up.