Paint Calculator
Calculate paintable wall and ceiling area, apply separate coat counts, and divide by the coverage stated for the exact coating and surface.
What does the paint calculator calculate?
Room paint equals net wall area times wall coats plus ceiling area times ceiling coats, divided by the product’s coverage per gallon. This calculator subtracts standard entered doors and windows, then rounds up to whole gallons. Calculate different colors, primers, and finishes separately.
Interior room paint formula
The wall perimeter produces gross wall area. Standard opening deductions create net walls; coat counts convert each surface into total coat-area before division by labeled gallon coverage.
How to measure for an accurate estimate
- Measure every wall length at the painted face and use the actual finished ceiling height.
- Replace the standard opening deductions with a separate area adjustment when doors or windows are unusually large.
- Treat vaulted ceilings, stairwells, built-ins, accent walls, and wainscot as separate measurable surfaces.
- Read expected coverage from the exact primer or paint label because formulation and substrate affect spread rate.
Two coats in a 14-by-12-foot room
A 14-by-12-by-8-foot room has one door, two windows, two wall coats, no ceiling paint, and 350-square-foot coverage.
Net walls total 365 square feet; two coats need 730 coat-square-feet, or 2.09 gallons, rounded to 3 gallons.Before you purchase material
- Calculate primers, wall colors, ceiling paint, and trim enamel separately because they are not interchangeable.
- Keep cans from one tint batch together and box mixed containers when color uniformity is critical.
- Use the manufacturer’s recommended applicator and film thickness rather than stretching paint beyond labeled coverage.
- Retain a small labeled amount for touch-ups, noting color, sheen, base, formula, and purchase date.
Common questions
How many square feet does a gallon of paint cover?
Many interior paints advertise a range near 350 to 400 square feet per gallon for one coat, but the exact rate belongs to the product label. Porous, rough, repaired, or dramatically recolored surfaces can reduce practical coverage.
Should I subtract doors and windows for paint?
Subtracting large unpainted openings improves the estimate. For small openings, the extra paint may offset brush and roller loss. This calculator uses 21 square feet per door and 15 per window; measure unusual openings directly.
Do two coats use exactly twice as much paint?
The planning formula doubles coated area, but real coats may spread differently because the first coat seals or changes the substrate. Follow labeled recoat directions and film thickness. Strong color changes or repaired surfaces may also require a separate primer.
Can leftover wall paint be used on the ceiling?
Only if the same product, sheen, color, and performance are appropriate and approved for that surface. Ceiling coatings often have different spatter, hide, and sheen characteristics. Calculate separate products independently when specifications differ.
Sources and reference standards
- U.S. Environmental Protection Agency — Lead RenovationFederal requirements and safety information for disturbing lead-based paint in covered pre-1978 properties.