How to use this calculator
- Enter Room length in ft.
- Enter Room width in ft.
- Enter Ceiling height in ft.
- Enter Coats — or tap a preset badge to auto-fill a typical value.
- Enter Coverage in sq ft/gal.
- Press Calculate. The highlighted row is your order quantity; the note beneath it translates the number into real-world terms.
Formula & constants
One gallon covers about 350 sq ft per coat on smooth primed walls. Wall area × coats ÷ 350 = gallons. A 12×12 room, two coats, walls only, needs two gallons. Every default in the fields above is editable — when your supplier’s spec sheet lists a different density, coverage rate or price, enter that number instead. The waste and compaction allowances follow common trade practice; see our methodology page for the derivation of each formula and the standards it references.
Where this fits in the project
Interior finishing runs framing-out: studs, insulation, drywall, then paint and floor coverings. Measure once and reuse the same wall and floor areas across each material takeoff.
How this connects to your project
No quantity stands alone — each material in the chain depends on the ones around it. These are the planning steps that pair with the paint calculator:
- Drywall Calculator — Paint covers drywall surfaces.
- Paint Cost Calculator — Estimate painting cost from gallons needed.
- Wallpaper Calculator — Paint vs wallpaper wall covering comparison.
- Insulation Calculator — Paint is surface finish; insulation is thermal barrier.
- Baseboard Calculator — Paint walls before or after baseboard installation.
- Crown Molding Calculator — Wall paint color affects crown molding contrast.
- Siding Calculator — Interior paint vs exterior siding finish.
Frequently asked questions
How much does a gallon of paint cover?
300–400 sq ft per coat depending on texture and porosity — 350 is the planning number.
Do dark colors need extra coats?
Deep bases and drastic color changes often need three coats; a tinted primer coat usually beats a third finish coat.
Last verified: — prices reflect current national averages. See our methodology.
Estimates are for planning. Material densities, coverage rates and prices vary by region and supplier — confirm final quantities before ordering, and check local code where structural or electrical work is involved.