Paint Calculator
Calculate how much paint you need for a room's walls and ceiling from its dimensions, number of coats, and your paint's coverage rate.
Enter your room's dimensions, the number of coats, and your paint's coverage rate to calculate how much paint you need.
How This Calculator Works
Wall area equals the room's perimeter times its wall height: 2 × (length + width) × height. This calculator uses that formula, then subtracts the area of any doors and windows you specify, since those openings aren't painted the same way as the surrounding wall.
If you include the ceiling, its area (length × width) is added to the total paintable area using the same room footprint. The combined area is then multiplied by the number of coats, since each additional coat requires the same amount of paint as the first.
Coverage rate is how much area one unit of paint (a gallon or a liter) covers in a single coat, printed on the paint can — it's usually around 350–400 square feet per gallon (32–37 square meters per equivalent volume), but drops noticeably on textured surfaces or unprimed drywall.
The calculated amount is the exact quantity needed for the area and coats specified. Since paint is sold in fixed can sizes, round the result up to the next available size — a small leftover amount costs far less than running out mid-job and needing to match a new batch's color.
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About this calculator
This calculator finds how much paint you need by combining the wall area of a room (from its length, width, and height) with the number of coats and the coverage rate printed on your paint can, then subtracting the area taken up by doors and windows. It works in both US units (feet and gallons) and metric units (meters and liters).
- Wall area from room dimensions — Computes total wall area from a room's length, width, and wall height, using the standard perimeter-times-height formula.
- Door and window deductions — Subtracts the area of doors and windows from the total, using standard reference sizes you can adjust to match your specific openings.
- Optional ceiling coverage — Add the ceiling to the total paintable area with a single toggle, using the same room footprint.
- Multiple coats — Set the number of coats to apply — most jobs need two — and the calculator multiplies the area accordingly.
- Adjustable coverage rate — Enter the coverage rate from your specific paint can (a typical default of 350 sq ft or about 32 m² per gallon/liter-equivalent is provided, but rates vary by paint type and surface).