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EnoughMath

Paint Calculator

Find how many gallons of paint your room needs — and the cheapest mix of cans to buy.

Units

A standard door is about 3 × 7 ft.

Printed on the can. Rough or porous walls cover less.

Result

Wall paint needed

1.90 gal

You need about 1.90 gallons of wall paint — buy 2 gallons.

Wall paint needed
7.2 L
Wall paint to buy
2 gallons
Paintable wall area
333.0 sq ft
Total wall area
384.0 sq ft

Shopping list

  • Wall paint: 2 gallons (2 coats)

Room length 12 ft · Room width 12 ft · Wall height 8 ft · Doors 1 · Area per door 21 sq ft · Windows 2 · Area per window 15 sq ft · Coats 2 · Coverage per gallon 350 sq ft/gal

Assumptions
  • Coverage of 350 sq ft per gallon per coat — the conservative end of typical US label ranges. Use the number on your can.
  • Doors are 21 sq ft and windows 15 sq ft each unless you change them.
  • Ceiling paint is listed separately because it’s often a different product.
  • Leftover quarts: one quart is listed as a quart; two or more become another gallon, since two quarts usually cost about as much as a gallon.

Estimates only. Check product labels and local building codes, and consult a licensed professional for structural, roofing or code-regulated work.

How to measure

  1. Measure the room’s length and width along the floor, in feet.
  2. Measure the wall height from floor to ceiling.
  3. Count doors and windows. The defaults are 21 square feet per door (about 3 × 7 ft) and 15 per window. Change them if yours are bigger or smaller.
  4. Check your can’s coverage. It’s printed on the label as square feet per gallon. Enter that number — it’s the biggest factor in the result.
A room with its length, width and wall height marked, plus a door and a windowRoom lengthRoom widthWall heightDoorWindow
Measure each wall at floor level. The calculator subtracts doors and windows using the sizes you enter.

How this calculator works

The calculator works out the wall area, takes away doors and windows, multiplies by the number of coats, and divides by your paint’s coverage.

  • Wall area = 2 × (length + width) × height
  • Paintable area = wall area − doors − windows (never below zero)
  • Gallons = paintable area × coats ÷ coverage per gallon
  • Buying plan: gallons are rounded up to whole quarts. One leftover quart stays a quart; two or three become another gallon. At five gallons or more, a 5-gallon bucket is suggested.

Example. Room length 12 ft · Room width 12 ft · Wall height 8 ft · Doors 1 · Area per door 21 sq ft · Windows 2 · Area per window 15 sq ft · Coats 2 · Coverage per gallon 350 sq ft/gal

Wall paint needed
1.90 gal
Wall paint needed
7.2 L
Wall paint to buy
2 gallons
Paintable wall area
333.0 sq ft
Total wall area
384.0 sq ft

You need about 1.90 gallons of wall paint — buy 2 gallons.

Before you buy

  • Use your can’s coverage, not ours. We default to 350 square feet per gallon, the low end of what Benjamin Moore lists for its interior paints (350–450). Lower is safer: you won’t run short.
  • Rough or textured walls? If your can lists a separate coverage for rough surfaces, use that number.
  • Primer. Follow the paint label on whether your surface needs primer. If it does, switch on Add primer and enter the primer’s coverage from its can.
  • Mix your cans together. For one color across several cans, pour them into one bucket and stir before you start — Dunn-Edwards shows the method for consistent color.

Questions

How much paint do I need for a 12 × 12 room?

With 8-foot walls, one door, two windows and two coats, about 1.9 gallons at 350 square feet per gallon — buy 2 gallons.

Should I buy quarts or another gallon?

If you'd need two or more extra quarts, the calculator rounds up to another gallon, because two quarts usually cost about as much as a gallon. One extra quart stays a quart.

Does the calculator include the ceiling?

Only if you switch it on. Ceiling paint is shown separately because it's often a different product.

Sources & methodology

  1. Dunn-Edwards — How to mix paint for color consistency
  2. Benjamin Moore — Ben Interior Paint, Matte: coverage 400–450 sq ft per gallon
  3. Benjamin Moore — Aura Interior Paint, Matte: coverage 350–400 sq ft per gallon

Last reviewed . How we build and test our calculators.