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Paint Calculator

Wall area × number of coats, divided by your paint's coverage rate.

Wall area (sq ft)

Coverage per gallon (sq ft)

Number of coats

Gallons needed

2.286 gal

Standard paint covers about 350-400 sq ft per gallon — check your specific can's label.

What you entered

Wall area (sq ft): 400Coverage per gallon (sq ft): 350Number of coats: 2

1
Total area to cover (accounting for coats)
400 × 2= 800 sq ft
2
Divide by coverage per gallon
800 ÷ 350= 2.2857 gallons

Result

Gallons needed: 2.286 gal

400 sq ft with 2 coats needs about 2.2857142857142856 gallons of paint.

Gallons of paint for common room sizes with 8 ft ceilings

Wall area is the room perimeter times an 8 ft ceiling with no deduction for doors or windows. The first two columns use the 350 sq ft per gallon rate printed on most cans; the last uses 300 sq ft per gallon, which is closer to what textured, unprimed or color-changing walls actually take.

Room size (ft)	Wall area at 8 ft ceiling (sq ft)	1 coat at 350 sq ft/gal	2 coats at 350 sq ft/gal	2 coats at 300 sq ft/gal
8 x 10	288	0.82	1.65	1.92
10 x 10	320	0.91	1.83	2.13
10 x 12	352	1.01	2.01	2.35
12 x 12	384	1.10	2.19	2.56
12 x 14	416	1.19	2.38	2.77
12 x 16	448	1.28	2.56	2.99
14 x 16	480	1.37	2.74	3.20
16 x 20	576	1.65	3.29	3.84
20 x 24	704	2.01	4.02	4.69

Paint is sold in whole gallons and quarts, so round up: a 2.19 gallon answer means three gallons, or two gallons plus a quart. Ceilings are extra and are not in these numbers, at roughly one gallon per 350 sq ft of ceiling for two coats. Primer is a separate purchase over new drywall, bare wood, patches, stains, or a dark-to-light change. Subtracting doors and windows would cut each figure by roughly 10 percent, and leaving them in is the cushion that keeps you from a second trip to the store. Keep the leftover for touch-ups, and buy all of one color in a single batch so the tint matches.

Coverage varies by paint and surface

Coverage claims on the can (usually 350-400 sq ft/gallon) assume a smooth, primed surface — textured walls, unprimed drywall, or dark-to-light color changes all reduce actual coverage, sometimes significantly.

Two coats is standard for a reason

A single coat rarely gives even, opaque coverage, especially over a different existing color — budgeting for two coats from the start avoids a mid-project paint store run.

Frequently asked questions

My room is 12x14 ft with 8-ft ceilings — how many gallons of paint do I need?

Wall area is about 416 sq ft. After subtracting ~40 sq ft for doors and windows, that's 376 sq ft. At 350 sq ft/gal coverage, two coats need about 2.15 gallons — buy 3 gallons to be safe.

Do I need primer in addition to paint?

Use primer on new drywall, bare wood, patched areas, stains, or when making a dramatic color change (dark to light). Self-priming paints ('paint and primer in one') work for repainting over similar colors on already-primed surfaces.

Why does one gallon cover less than the can says?

Can labels assume a smooth, primed, same-color surface (typically 350-400 sq ft/gal). Textured walls, unprimed surfaces, and color changes reduce actual coverage by 10-30%. Use 300 sq ft/gal for realistic estimates on imperfect surfaces.

How much paint do I need for the ceiling?

Calculate ceiling area separately (length x width of the room). Ceilings typically need the same 2 coats as walls. A 12x14 room has 168 sq ft of ceiling, which takes about 1 gallon for two coats.