RightFiguresWalls, minus the openings you enter
The wall area is twice the sum of the room length and width, times the wall height. Subtract the opening area you enter, multiply by the number of coats, and divide by the coverage of the paint you are using.
Bellevue’s painting guidance says to measure the area first, that a textured surface needs more paint, and that the coverage to read is the coverage on the can. That is why coverage is an input. This page does not pick a brand or a price. Room dimensions use the international foot from NIST Appendix B.
The concrete calculator estimates a slab volume. The flooring calculator counts boxes. Neither one estimates paint.
A 12 by 10 foot room
A room 12.00 feet by 10.00 feet with 8.00 foot walls has 352.00 square feet of wall. Subtract 48.00 square feet of openings and 304.00 square feet remain. Two coats at 350.00 square feet per gallon are exactly 608/350 gallons. The display is 1.74 gallons. The purchase count is 2 gallons.
The displayed gallons are not the purchase count
A room 10.00 by 2.55 feet with 10.00 foot walls, no openings, one coat, and 250.00 square feet per gallon is exactly 1.004 gallons. The display is 1.00 gallons. The purchase count is still 2 gallons, because the ceiling uses the exact amount.
5.00 by 5.05 feet, 10.00 foot walls, one coat, and 200.00 square feet per gallon is exactly 1.005 gallons. That displays as 1.01 gallons and still buys 2 gallons. When the exact amount is already a whole number of gallons, the ceiling does not add another gallon.
Openings that use the whole wall
The same 10.00 by 2.55 by 10.00 foot room has 251.00 square feet of wall. Entering 251.00 square feet of openings leaves 0.00 square feet to paint, so the gallon count is 0. Entering 251.01 is larger than the wall, and no gallon count is shown. Width cannot be 0 to mean one wall.
Above 1,000,000 gallons
A 1,000.00 by 1,000.00 foot room with 30.00 foot walls, 10 coats, and 0.01 square feet per gallon is above 1,000,000 gallons. No count is shown. A 100.00 by 100.00 foot room with 25.00 foot walls, one coat, no openings, and 0.01 square feet per gallon is exactly 1,000,000 gallons, and that count is shown.
Frequently asked questions
Does this page know how much a can covers?
No. Read the coverage on the can, or the rate for the surface you are
painting, and enter that number. A textured surface can need more paint than a
smooth one.
Why can the gallons figure be lower than the number to buy?
The gallons figure is rounded half up for display. The whole-gallon count is
the exact amount rounded up. Buying the displayed figure can be short.
Are the room dimensions sent to analytics?
No. Analytics may record that this calculator ran. Dimensions, openings,
coats, coverage, and the gallon counts stay in this browser.
Sources & review
- Painting and Paint Recycling — City of Bellevue
- Guide to the SI, Appendix B — National Institute of Standards and Technology
Last reviewed: . The formula is reproduced above so you can check the math independently.
Educational estimate only. This page does not choose a coverage rate, a brand, or a price.