Paint Calculator

Find out how many gallons of paint (and optional primer) you need to paint a room. Enter the room dimensions, openings and number of coats; coverage per gallon and prices are editable to match your paint can.

Project size
ft
ft
ft
doors
windows
Assumptions
coats
sq ft
Use the coverage on your paint can label.
sq ft
sq ft
3 ft × 7 ft = 21 sq ft.
sq ft
3 ft × 5 ft = 15 sq ft.
Unit prices editable estimates

Default prices are placeholder estimates, not quotes or sourced data. Replace them with your local prices.

$
$
$
%

Materials & cost estimate

Paintable wall area
333 sq ft
Ceiling area
Not included
Paint needed (exact)
1.9 gal
Paint to buy
2 gal

Materials

MaterialQtyUnit priceEst. cost
Paint (2 coats)2 gallons$42.00$84.00
Supplies (rollers, brushes, tape, tray)1 set$35.00$35.00
Subtotal$119.00

Estimated cost range: $101.15 – $136.85

Buy these materials

Affiliate links (placeholders): if you buy through these links we may earn a commission at no extra cost to you. Quantities come from your inputs above.

  • Ceilings are often painted with a different (flat ceiling) paint; this calculator prices it at the same per-gallon price.
  • Textured, porous or dark-to-light color changes may need more coats or primer.

Prices are editable estimates, not quotes. Always confirm quantities, structural requirements and local prices before buying.

Key facts

  • Wall area of a rectangular room = 2 × (length + width) × wall height.
  • A 12 × 12 ft room with 8 ft walls, one door and two windows has about 333 sq ft of paintable wall.
  • At 350 sq ft per gallon, two coats on 333 sq ft of wall take 1.9 gallons of paint.
  • Gallons of paint = paintable area × number of coats ÷ coverage per gallon.

How it's calculated

The paint calculator uses these formulas (⌈x⌉ means round up, ⌊x⌋ means round down). Quantities are rounded up to whole items you can buy.

  1. Paintable wall area = 2 × (length + width) × height − doors × door area − windows × window area
  2. Ceiling area = length × width (if included)
  3. Paint gallons = (wall area + ceiling area) × coats ÷ coverage per gallon
  4. Gallons to buy = ⌈ paint gallons ⌉
  5. Primer gallons = (wall area + ceiling area) ÷ primer coverage (if included), rounded up to buy
  6. Cost = Σ (quantity × unit price) + supplies; range = cost × (1 ± range % ÷ 100)

Default unit prices come from this site's editable defaults file (/api/prices.json), last reviewed 2026-10-20. They are placeholder estimates, not sourced market data.

Worked example

A 12 ft × 12 ft room with 8 ft walls has 2 × (12 + 12) × 8 = 384 sq ft of wall. Subtracting 1 door at 21 sq ft and 2 windows at 15 sq ft leaves 333 sq ft. 2 coats at 350 sq ft per gallon need 333 × 2 ÷ 350 = 1.9 gallons, so buy 2 gallons. At the default editable prices the subtotal including supplies is $119.00 (range $101.15 to $136.85).

Frequently asked questions

How many gallons of paint do I need for a room?

Multiply the paintable area by the number of coats and divide by the coverage on the can. For example, about 333 sq ft of wall with two coats at 350 sq ft per gallon needs about 1.9 gallons, so you would buy 2.

How much does one gallon of paint cover?

Coverage varies by product and surface; check the label on your can. This calculator defaults to 350 sq ft per gallon, which you can change.

Do I need two coats of paint?

Two coats are common for even color and durability, especially when changing colors. Some paint-and-primer products claim one-coat coverage; results depend on the surface and color.

Should I subtract doors and windows?

Yes, for a closer estimate. The defaults use 21 sq ft per door (3 × 7 ft) and 15 sq ft per window (3 × 5 ft); edit them to match your openings.

Are the prices accurate?

No. Default prices are placeholder estimates. Enter the per-gallon price of the paint you plan to buy.

Other calculators

Cite this tool: “Paint Calculator”, EstimaHome, https://estimahome.com/paint-calculator/ (updated 2026-10-20). Machine-readable spec: /api/calculators.json.