Is this only an estimate?

Yes. Product sizes, coverage, waste, cuts, surface condition, and supplier rules can change the final amount.

Construction calculator

Paint Calculator

It uses the formula: gallons = paintable wall area x coats / coverage per gallon.

Estimate paint needed for interior rooms using wall dimensions, coats, coverage per gallon, and door or window deductions.

Paint estimate

Room length

Room width

Wall height

UnitCoats

Coverage

sq ft/gal

Doors/windows

sq ft

Paint to buy

2 gal

Estimated use is 1.78 gallons.

Wall area

352 sq ft

Before subtracting openings

Paintable area

312 sq ft

After doors/windows

Coated area

624 sq ft

Paintable area x coats

gallons = paintable wall area x coats / coverage per gallon

Coverage varies by paint type, wall texture, primer, color change, and surface condition. Round up before buying.

Input	Estimate
12 ft x 10 ft room, 8 ft walls, 2 coats	About 1.11 gallons before rounding
350 sq ft/gallon coverage	Common planning estimate
Subtract 40 sq ft openings	Allows for doors and windows