Paint Calculator

How many gallons or liters of paint for a room: wall area minus doors and windows, optional ceiling, number of coats and coverage rate.

A 3 × 7 ft door ≈ 21 ft².
A 3 × 5 ft window ≈ 15 ft².
Check the can. Typical interior latex labels say 350–400 ft²/gal (Benjamin Moore Regal Select: 400–450). 350 ft²/gal ≈ 8.6 m²/L. Use less for rough or porous surfaces.
%
Covers roller and tray loss and touch-ups.
$per gallon
Your rate is remembered on this device.
Paint needed
1.81
1-gallon cans to buy
2 cans
Paintable area (one coat)
301
Estimated paint cost
$90.00
Paint only (whole gallons). Primer, tape and tools are extra.

Estimate generated with SortedSums: https://sortedsums.com/paint-calculator/. For informational purposes only; verify before relying on it.

Estimate only. This tool is for informational and educational purposes. Results depend on your inputs and simplifying assumptions, and are not a substitute for professional engineering, design or financial advice. Always verify with a qualified professional and applicable codes before purchasing, building or making decisions.

How it’s calculated

Wall area = 2 × (length + width) × height − doors − windows Gallons = area × coats × (1 + waste%) ÷ coverage (ft²/gal)

Example: a 12 × 10 ft room with 8 ft walls = 2 × 22 × 8 = 352 ft². Subtract one 21 ft² door and two 15 ft² windows → 301 ft². Two coats with 5% extra = 632.1 ft² ÷ 350 ft²/gal = 1.81 gallons (6.8 L), so buy 2 gallons.

Coverage on the label assumes a smooth, primed surface. New drywall, bare wood, texture and big color changes all use more paint.

Frequently asked questions

How much does a gallon of paint cover?

Most interior latex paints list 350–400 ft² per gallon for one coat on a smooth surface; some premium lines list 400–450. Rough or porous surfaces may get only 250–300.

How many gallons of paint for a 12x12 room?

With 8 ft walls: 2 × 24 × 8 = 384 ft², minus a door and two windows ≈ 333 ft². Two coats at 350 ft²/gal ≈ 1.9 gallons, so 2 gallons for the walls.

Do I need two coats of paint?

Usually yes for an even finish, especially when changing color or painting new drywall (which should also be primed).

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Sources

Formulas are taken from the free public references above. Results are provided “as is” for informational and educational purposes only. See our disclaimer.

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