Paint Coverage Calculator
Calculate how much paint you need for a room
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Paint Coverage Calculator helps you calculate how much paint you need for a room without a spreadsheet. Just enter Room Width (ft), Room Length (ft) and Ceiling Height (ft); Paint Coverage updates the result as you type. Nothing in Paint Coverage is a black box. Paint Coverage suits budgeting and planning checks. Paint Coverage is privacy-first: Lifestyle inputs stay offline. Looking for paint coverage calculator or free online paint coverage calculator? Paint Coverage covers both. Keep Paint Coverage bookmarked for next time. Start with Paint Coverage; the first number takes seconds.
What the defaults give
A 12 × 14 ft room with an 8 ft ceiling has 416 sq ft of wall.
Taking off 30 sq ft of windows and 40 sq ft of doors leaves 346 sq ft, which is 2 gallons for two coats.
The formula
Wall area = 2 × (width + length) × height
Net area = wall area − windows − doors
Gallons = net area × coats ÷ 350
2 × (12 + 14) × 8 = 416 sq ft. 416 − 30 − 40 = 346. Two coats is 692 sq ft, and 692 ÷ 350 = 1.98, rounded up to 2 gallons.
Worked examples
12 × 14 × 8, 70 sq ft openings, 2 coats → 2 gal
10 × 12 × 8, 70 sq ft openings, 2 coats → 282 × 2 ÷ 350 = 1.61 → 2 gal
10 × 12 × 8, 70 sq ft openings, 1 coat → 282 ÷ 350 = 0.81 → 1 gal
20 × 20 × 9, 150 sq ft openings, 2 coats → 720 − 150 = 570 × 2 ÷ 350 = 3.26 → 4 gal
12 × 14 × 8, no openings, 2 coats → 416 × 2 ÷ 350 = 2.38 → 3 gal
Why subtract the openings
Windows and doors are not painted, and their area is not trivial: 70 sq ft in a 346 sq ft job is a fifth of the surface. Skipping the subtraction overstates the paint by roughly a fifth, which on the defaults is most of a gallon. Measure the glass and the door leaves only — the frames and trim are painted, but with a different product.
Where the 350 figure comes from
Most interior wall paints cover about 350 square feet per gallon per coat on a smooth, primed surface. That is an average, and it moves in both directions:
- Texture. New drywall, stucco and heavy roller nap consume noticeably more.
- Colour change. Going from dark to light or to a strong colour usually needs an extra coat beyond what the area predicts.
- Primer. Bare or patched walls need a primer coat that the topcoat estimate does not include.
- Ceilings. Not counted here, since they are often a different product and a separate calculation.
- Wastage. Paint left in the tray, in the roller and in the tin does not go on the wall, so rounding up is normal.
Buy one extra gallon on a large job rather than stop mid-wall, and keep the batch code so a later top-up matches the colour.
Frequently Asked Questions
How much paint for a 12 by 14 room?
Two gallons for two coats, after calculating 416 sq ft of wall, subtracting 70 sq ft of openings and dividing by 350 sq ft per gallon.
Should I subtract windows and doors?
Yes. They are not painted, and their area is a meaningful fraction of the wall — about 17% in the default room.
How many square feet does a gallon cover?
Roughly 350 per coat on a smooth surface. Textured walls and strong colour changes reduce that.
Do I need to count the ceiling?
Not in this calculation. Ceilings are usually a different paint and a different coverage rate, so measure them separately.
Is two coats always enough?
Usually for a similar colour. A dramatic change or a dark-to-light repaint often needs a third, and primer may be required on bare wall.
Why round up rather than down?
Because paint cannot be stretched and a part-used wall looks worse than an extra gallon. The leftover also serves as touch-up paint.
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