Construction Calculators
Paint Calculator for Walls and Ceilings
Estimate whole gallons of paint and primer from room dimensions, openings, coats, and the coverage rate on your paint can. Results update as you change an input.
Inputs
Paint needed
Fill the form and press Calculate.
How to estimate paint for a room
Quick answer: enter the room length, width, and ceiling height; then set the openings, coats, and coverage rate. On a phone, work from top to bottom and check the Paint needed result before adding primer or the ceiling.
The estimate uses wall area minus the selected openings, plus ceiling area when requested. It rounds paint and primer up separately to whole gallons. Planning more of the room? Check sheet quantities with the drywall calculator, compare wall covering with the wallpaper calculator, or estimate framing volume and cost with the lumber calculator.
Coverage source checked October 3, 2026: Sherwin-Williams gives typical coverage of 350–400 sq ft per gallon for paint and 200–300 sq ft per gallon for primer, while noting that application method and surface condition change real coverage. Your product label wins. The displayed cost is only a rough planning figure using fixed CAD rates of $60 per paint gallon and $45 per primer gallon.
Paint calculator FAQ
How does this paint calculator estimate gallons?
It multiplies the room perimeter by ceiling height, subtracts the selected doors and windows, adds the ceiling if selected, and multiplies by the number of coats. It then divides by your coverage rate and rounds up to whole gallons.
Does the paint estimate include doors, windows, and the ceiling?
The wall estimate subtracts 21 square feet for each door and 15 square feet for each window. The ceiling is excluded unless you select Paint ceiling.
Can I change the number of coats and coverage per gallon?
Yes. Enter the coats you plan to apply and the coverage rate shown for your paint. The calculator uses both values directly in the estimate.
How is primer calculated?
When Use primer is selected, the calculator estimates one primer coat over the same paintable area, uses the separate primer coverage rate you entered and rounds up to whole gallons.