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Open toolPaint Calculator
Estimate wall-paint volume from room dimensions, openings, coats, and coverage. Review gallons, litres, and the whole gallons to buy.
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How Paint Calculator works
Paintable wall area is scaled by coats, allowance, and product coverage.
The calculator finds the perimeter of the rectangular room, multiplies it by wall height, and subtracts openings. That paintable area is multiplied by coats and allowance, then divided by coverage per gallon.
Estimates wall paint only. Check the paint label for actual coverage, especially for textured or porous surfaces.
How to use Paint Calculator
This estimate covers rectangular room walls, with separate openings, coats and coverage inputs.
Enter the room and coating assumptions
Enter room length, width, and wall height in feet, then the doors-and-windows area in square feet. Set coat count, coverage per gallon, and extra allowance. Use the intended paint’s stated coverage rather than treating the example input as a product guarantee.
Room length
Calculate the paint volume
Select Calculate and read the estimated gallons needed for the walls. The page subtracts openings from the four-wall area before applying coats, allowance, and coverage. It asks for corrected inputs if openings remove all the calculated wall area.
0.98 gal
Review purchase rounding and coverage
Check Whole gallons to buy, Litres, and Paintable wall area with the main estimate. Whole gallons round the estimated volume upward. Ceilings, surface texture, application conditions, and actual product coverage need their own review outside this rectangular-wall model.
Whole gallons to buy
Situations for a wall paint estimate
Use separate calculations when surfaces or products need different coverage assumptions.
Estimate one rectangular room
Use the room dimensions and opening areas to create a wall only quantity. Keep ceiling paint and trim outside the result. This makes it easier to reconcile the area with your own room sketch and the surfaces actually being painted.
Compare one coat and two coats
Keep area, coverage and allowance fixed while changing the coat count. The resulting quantity reflects the additional application over the same area. The page does not decide how many coats a surface requires or assess whether a finish has covered adequately.
Inspect a coverage assumption
Enter two coverage values while holding the room and coat count constant. A lower coverage value requires more paint for the same area. Check the product label and surface conditions rather than treating a generic coverage value as a guarantee.
Estimated gallons and whole gallons
Read estimated volume separately from the rounded purchase quantity.
Estimated paint needed is the calculated liquid quantity with the entered allowance. Whole gallons to buy rounds that quantity upward to the next whole gallon; it does not choose a retailer's package sizes or combination of containers.
Paintable wall area is the rectangular wall area minus entered openings. The litres line converts the estimated gallons. These outputs use different units, so retain their labels when transferring the estimate into a shopping list.
Check area and actual spread rate
Check opening area, coverage, and excluded surfaces before ordering paint.
The form rejects openings that leave no positive wall area. Check whether the openings field contains a combined square foot area rather than a width or a count of windows. Keep lengths in their own dimension fields.
Textured or porous surfaces can differ from the assumed coverage. The calculator does not assess the substrate or product application. Confirm the actual spread rate and account separately for ceilings and trim before relying on the quantity.
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Open toolUse Paint Calculator
Estimate wall-paint volume from room dimensions, openings, coats, and coverage.
Paint Calculator: common questions
Answers about using Paint Calculator and understanding its results.
Is the ceiling included?
No. This calculates the four walls of a rectangular room.
Why might I need more paint?
Texture, colour changes, application method, and surface condition affect coverage.
Why are whole gallons higher than the volume estimate?
The purchase quantity rounds the estimated gallons upward to a whole number. The precise estimated volume is shown separately.
What happens if openings exceed the wall area?
The page asks you to correct the dimensions or openings. The paintable wall area must be greater than zero.