Paint quantity estimator

How to use the paint quantity estimator

Estimate how many gallons of paint a rectangular room may need from its dimensions, ceiling height, and number of coats. Use the quick estimate for budgeting before measuring doors, windows, primer, or trim separately.

1. Select a preset under Room size, or choose Custom size.
2. Enter the Ceiling height in feet.
3. If you chose Custom size, enter the Room length and Room width in feet.
4. Set the number of Coats.
5. Turn on Include the ceiling if the ceiling will be painted, then review the typical estimate and range.

What to enter

Room size

Choose Small (10 × 10 ft), Medium (12 × 14 ft), Large (16 × 20 ft), or Custom size. The default is Medium (12 × 14 ft).

Ceiling height

Enter the wall height in feet. The default is 8 ft. The interface accepts 6–20 ft in 0.5-ft steps.

Room length

Shown for Custom size. Enter the room length in feet. The default is 12 ft, with a minimum of 1 ft and 0.5-ft steps.

Room width

Shown for Custom size. Enter the room width in feet. The default is 14 ft, with a minimum of 1 ft and 0.5-ft steps.

Coats

Enter a whole number from 1 to 5. The default is 2 coats.

Include the ceiling

Turn this on to add the room’s length × width as ceiling area. It is off by default.

Example: medium room, two coats, no ceiling

Use the default Medium room: 12 × 14 ft, an 8-ft ceiling, 2 coats, and Include the ceiling off. Wall area is 2 × (12 + 14) × 8 = 416 sq ft. Ceiling area is 0 sq ft, so total area is 416 + 0 = 416 sq ft. Across two coats, the painted area is 416 × 2 = 832 sq ft-coats. At the typical 350 sq ft/gal coverage, 832 ÷ 350 = 2.377... gal, displayed as 2.38 gal. The purchase amount rounds to 2.5 gal. At 400 sq ft/gal, 832 ÷ 400 = 2.08 gal, which rounds to 2.25 gal. At 300 sq ft/gal, 832 ÷ 300 = 2.773... gal, displayed as 2.77 gal, which rounds to 3 gal. The result is a 2.5-gal quick estimate and a 2.25–3 gal purchase range.

How the estimate is calculated

For a rectangular room, wall area is 2 × (room length + room width) × ceiling height. If Include the ceiling is on, ceiling area is room length × room width; otherwise it is 0. The tool adds these areas and multiplies by the number of coats. It divides the result by 350 sq ft/gal for the typical estimate, by 400 sq ft/gal for the low amount, and by 300 sq ft/gal for the high amount. Displayed exact quantities are rounded to two decimals. Purchase quantities are rounded up to quart or gallon increments: a fractional gallon below 0.5 is rounded up to the next quarter gallon, while a fractional remainder of 0.5 or more is rounded up to the next whole gallon. The can mix uses 5-gallon buckets, 1-gallon cans, and quarts.

Reading the results

Quick estimate is the purchasable amount based on 350 sq ft/gal. Range shows the purchasable low and high amounts based on 400 and 300 sq ft/gal. Area to paint includes the selected wall area and, when enabled, the ceiling area. The breakdown also shows the displayed exact amounts before purchase-size rounding.

Limitations and common mistakes

• The quick estimate ignores doors and windows, so it does not subtract their area.
• It does not add separate amounts for primer or trim.
• The calculation assumes a rectangular room with one ceiling height and uses the tool’s coverage assumptions: 350 sq ft/gal typically, with 300–400 sq ft/gal as the range.
• Inputs and results on this tool use feet and US gallons; custom length and width are used only when Room size is set to Custom size.

Frequently asked questions