Estimate how many gallons of paint you need for walls, ceilings, and trim. Accounts for doors, windows, and number of coats. Includes cost estimation.
Paint estimation is one of the most common DIY math problems and one of the easiest to get wrong. Buy too little and you have to make a second store trip mid-job (often with paint that doesn't exactly match if it's a custom tint). Buy too much and you have $40+ of paint sitting in the garage going stale. The math is straightforward once you know the right coverage numbers.
This calculator computes paint quantity for interior rooms: walls only, walls + ceiling, accounting for doors and windows, with multiple coats. The standard assumption is 350 square feet covered per gallon with one coat — slightly conservative compared to the 400 sq ft on the can label, but more realistic for the cutting-in, brush loss, and over-application that happens during real painting.
For most rooms, you'll need 1–2 gallons per coat for walls, plus an additional gallon for ceilings if included. Most interior paint jobs need two coats unless you're refreshing the same color or doing touch-ups.
14 × 12 × 8 ft bedroom, 2 doors, 2 windows, 2 coats, no ceiling. Wall area: 2 × 26 × 8 = 416 sq ft Net (after openings): 344 sq ft With 2 coats: 688 sq ft Gallons: 688 / 350 = 1.97 → 2 gallons At $40/gallon: $80 in paint, plus rollers, brushes, primer, and drop cloths if you don't already have them.
Same bedroom + ceiling, 2 coats. Adding ceiling area: 168 sq ft × 2 coats = 336 sq ft Total: 688 + 336 = 1,024 sq ft Gallons: 1,024 / 350 = 2.93 → 3 gallons Ceiling paint is often a different (cheaper, flatter) formula than wall paint, so you may buy 1 gallon ceiling + 2 gallons wall.
Use this calculator for any interior paint job: bedrooms, living rooms, hallways, ceilings. The same math works for exterior siding (with adjusted coverage — exterior paint typically covers ~300 sq ft per gallon due to texture).
Add to gallons for: - Heavily textured walls (orange peel, knockdown): +10% - Porous surfaces (fresh drywall, raw wood): need primer first - Dark-to-light color change: use a primer + tinted to a midtone, then 2 coats of color - High-quality paint may need only 1 coat on similar-color jobs
Don't forget supplies: - Painter's tape (for crisp lines): 1 roll per 60–80 ft of trim - Drop cloths: 1 per room minimum - Rollers: 1 cover per gallon, or per ~350 sq ft - Brushes: 2–3 inch angled sash brush + 1 small detail brush - Primer: ½ gallon per 200 sq ft of bare/dark areas
For paint cost estimation including supplies, budget about 20–30% above the paint-only cost on a first-time job.
Calculate the square footage of rooms, walls, and irregularly shaped areas.
Calculate rolls of wallpaper needed for a room.
Calculate sheets of drywall needed for walls and ceilings.
Calculate roofing squares, bundles of shingles, and materials needed.
Calculate flooring material needed with waste factor for any room.
Calculate fence materials including posts, rails, pickets, and concrete.
Gallons to Buy
2
Paintable Area
344 sq ft
Estimated Cost
$80.00
| Item | Area | Note |
|---|---|---|
| Wall Area (gross) | 416 sq ft | 52 ft perimeter x 8 ft height |
| Door Deduction | -42 sq ft | 2 door(s) x 21 sq ft |
| Window Deduction | -30 sq ft | 2 window(s) x 15 sq ft |
| Net Paintable Area | 344 sq ft | |
| Coverage (2 coats) | 688 sq ft | 350 sq ft/gallon coverage |