Paint Calculator
Estimate wall area, exact gallons needed, and rounded gallons to buy from room dimensions, coats, and paint coverage.
Last updated: 2026-03-27
Paint calculator
Enter your values
Estimate how many gallons of wall paint to buy before heading to the store.
Gallons To Buy
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Enter the room dimensions, wall height, coats, and coverage rate to estimate wall paint quantity.
Calculation History(0)
Example calculations
Tap an example to prefill the calculator with sample values.
Bedroom repaint
14 ft x 12 ft room at 8 ft walls
A standard bedroom where two coats usually push the project beyond the “one gallon should be enough” mindset.
Result: The wall-only estimate usually lands around a few gallons once both coats are counted honestly.
Large living room
22 ft x 18 ft room with 9 ft walls
A bigger open room where height and perimeter drive coverage much faster than floor area alone suggests.
Result: Big rooms become multi-gallon projects quickly, especially when you want a clean second coat.
Accent-room refresh
10 ft x 10 ft room with one finish coat
A smaller project where exact gallons matter because a gallon-plus-quart decision may feel more reasonable than buying extra gallons.
Result: Smaller rooms can still exceed one gallon once coverage and touch-up buffer stop being wishful thinking.
How the paint estimate works
The calculator converts room length and width into wall perimeter, multiplies that by wall height to get the wall area, then multiplies again by the number of coats. That is the total painted square footage your project needs to cover.
It then divides that coverage requirement by your chosen paint-coverage assumption to get an exact gallon estimate, while also rounding up to a practical buy quantity. This version stays intentionally conservative because it does not subtract openings or ceiling exclusions.
Paint calculator FAQs
Understand why wall area, not floor area, drives the number and why this version leans slightly conservative.
Why does the calculator use room dimensions instead of floor area?
Because wall paint covers vertical surface area, not the floor. The perimeter of the room multiplied by wall height is the useful starting point for estimating how much paint the walls actually need.
Does this include the ceiling?
No. This version is intentionally walls only. Ceiling paint is usually handled as a separate estimate because it may use different paint, a different sheen, or a separate coat count.
Why are doors and windows not subtracted?
To keep the workflow inside the 5-input cap and slightly conservative. For many quick DIY paint runs, a modest overestimate is more helpful than running short halfway through the second coat.
Embed this calculator
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Optional: auto-resize script
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</script> Related tools
Pair interior wall planning with other room-finish and renovation calculators.
Wallpaper Calculator
Plan another wall-finish project using roll-based strip math instead of paint coverage.
Tile Calculator
Estimate adjacent finish material if the same room is getting a broader surface refresh.
Insulation Calculator
Use another wall-focused planning tool if the room is being opened up before repainting.
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Walls-only estimate
This v1 estimate covers four full walls only. It does not subtract doors or windows and it does not include ceiling paint.