Paint Calculator — ft, sq ft, gallons & cost
How to use this calculator
Pick a surface mode — room walls, ceiling, a single wall, or a known area. Enter dimensions in feet and inches, choose the finish and number of coats, and a standard door (21 ft²) and window (12 ft²) are deducted per opening. Net gallons are rounded up to whole cans, since paint is sold by the can.
Paint types — Flat/Matte (400 ft²/gal), Eggshell (350), Satin (350), Semi-Gloss (350), Gloss (300).
Primer — 1 coat at 300 ft²/gal for new drywall, dark-to-light color changes, or stain blocking.
Cost — price per gallon of paint and primer, plus optional flat-rate for supplies (rollers, brushes, tape, drop cloths).
Saved Calculations
| Time | Mode | Area ft² | Paint gal | Primer gal | Coats | Total $ |
|---|
How to Estimate Paint for a Room
For a four-wall room the paintable area is the wall perimeter times ceiling height, less openings. This tool uses manufacturer coverage figures: a single gallon rolls roughly 350–400 ft² per coat on primed drywall, less on porous or textured surfaces. Two coats is the practical default for color over a similar base; budget three when going dark, covering bold color, or working with deep accent bases. After fresh drywall installed and taped, prime first so the topcoat covers evenly and the gallon count stays accurate.
How to use this calculator
Choose the surface mode, enter feet/inches, set the finish and coats, and add doors and windows so their area is removed. Set a waste allowance — 3% for smooth drywall, 5% typical, 10% for heavy texture or cut-in-heavy rooms. Open the cost panel for a per-gallon estimate; the supplies field is a flat job rate for rollers, brushes, tape and drop cloths. Working in metric? Use the paint calculator in m and liters.
Formulas Used
Paintable area = wall perimeter × height − doors − windows.
Paint gallons = ceil(paintable area × coats × (1 + waste%) ÷ coverage per gallon).
Primer gallons = ceil(paintable area × (1 + waste%) ÷ 300).
Paint Coverage by Finish
Flat/Matte: 400 ft²/gal — best for ceilings and low-traffic areas. Eggshell: 350 ft²/gal — most popular for living rooms and bedrooms. Satin: 350 ft²/gal — kitchens, bathrooms, hallways. Semi-Gloss: 350 ft²/gal — trim, doors, cabinets. Gloss: 300 ft²/gal — high-moisture areas and accent surfaces.
FAQ
Do I need primer? Yes for bare drywall, dark-to-light changes, or stain blocking — one coat at ~300 ft²/gal usually suffices. Self-priming paint can replace it on previously painted, sound surfaces in similar colors.
What about the floor and other finishes? Paint covers walls and ceilings only. For the floor see the flooring box calculator or carpet by square yard, and for backsplashes and wet areas the tile and grout calculator. Painting a masonry surface? Block and brick are far more porous — size the wall first with the block wall calculator and expect coverage near the low end.
On paint day
Three things estimators forget. Same batch, same can — buy all the gallons of one color at once and box them (pour into a 5-gallon bucket and stir) so the lap on the last wall matches the first; mid-can shifts are the #1 callback. Sheen and porosity — bare drywall, fresh joint compound, and unsealed wood drink the first coat, so spec primer in the takeoff or expect 30–50% more topcoat than the 350–400 ft²/gal label number. Cost basis (2025 USA) — mid-grade interior latex runs $35–55/gal, primer $25–40/gal, and pro labor adds $1–3/ft² for walls or $2–5/ft² for trim & doors. EPA RRP rule applies to pre-1978 homes — budget for lead-safe containment when scraping or sanding.
