Paint Calculator
Find out how much paint you need for a room — based on wall dimensions, doors, windows, and the number of coats.
With 414 sq ft of paintable wall and 2 coats, you'll need 2.37 gal of paint.
Paint to buy
Results update as you type. Coverage assumes a typical emulsion at ~350 sq ft/gal; check the tin/can label — porous surfaces, dark-to-light colour changes, and primer coats all need more paint.
Formula
Wall area is perimeter × height:
2 × (length + width) × height.
Subtract the typical area for each door and window (1.85 m² and 1.4 m² respectively),
multiply by coats, and divide by coverage (~11 m²/L for emulsion, ~350 sq ft/gal for US).
The calculator rounds up to whole tins because partial cans don't sell.
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Frequently asked questions
How many sq ft does a gallon of paint cover?▾
Most US wall paint advertises 350–400 sq ft per gallon per coat. The calculator uses 350 sq ft/gal as a conservative default — real-world coverage is often less because of texture, color changes, and DIY brushwork. Always buy a little extra; running out mid-wall is far worse than having half a quart left over.
How many coats do I need?▾
Two coats for most jobs. Three coats (or two over a tinted primer) for: dark over light, light over dark, fresh drywall, or stained surfaces. One-coat paints work in limited circumstances (same color, premium product) but rarely look as good as the marketing claims.
Should I include the ceiling?▾
Not in this calculator — wall area only. For ceilings, calculate length × width separately. Ceiling paint is usually a different product (flat finish, non-drip, low-spatter) and worth buying separately — using wall paint on a ceiling tends to drip and leave roller marks.
What about primer?▾
Primer is a separate purchase and a separate calculation. As a rough rule, primer covers roughly the same area per gallon as the wall paint that goes over it. For new drywall, water-stained walls, or strong color shifts, primer is essential; for repaints in similar colors over good substrate, you can usually skip it.
Is one gallon enough for a small bedroom?▾
Usually yes for a single coat in a typical 12×12 ft bedroom (~432 sq ft of wall after deductions, well under a single gallon's 350 sq ft). For two coats in that room, plan on about 1 gallon plus a quart, or just two 1-gallon cans.
How much extra should I buy for waste?▾
The calculator is already conservative on coverage. For unusually textured walls, popcorn ceilings (don't paint these — they often need replacement), or aggressive color changes, add ~15% on top of the calculated quantity. Sealed leftover paint stores ~2 years and is invaluable for touch-ups.