What this calculator does
The Paint Calculator tells you how much paint you need to paint a room. Enter the room's length, width and wall height; the calculator works out the total wall area, subtracts standard door and window openings (or adds the ceiling if you include it), multiplies by the number of coats, and converts the result into liters or gallons of paint using the coverage printed on the paint can. If you enter a price, it also estimates the total cost.
It works with metric (meters) and imperial (feet) room dimensions, and with coverage quoted either in square meters per liter or in square feet per gallon. The page is available in English, Arabic, and Spanish.
How to use the Paint Calculator
- Enter the room dimensions (length, width, wall height) in meters or feet. For L-shaped or multi-room jobs, run the calculator once per room and add the paint amounts together.
- Set the number of doors and windows. The calculator subtracts a typical door (1.6 m² / 17 ft²) and window (1.2 m² / 13 ft²) for each one. If your openings are much larger or smaller, adjust the counts to compensate.
- Tick "Include ceiling" if you are painting it too. The ceiling area is length × width.
- Set the number of coats (2 by default). Dark colors over light walls, or dramatic color changes, often need 2–3 coats.
- Enter the paint coverage exactly as printed on the can — typically 8–12 m² per liter, or about 350–400 ft² per gallon for a first coat. Rough or heavily textured walls need the lower end.
- Optionally enter the price per liter or per gallon to see the estimated cost. Paint is bought in whole cans, so the cost uses whole liters/gallons rounded up.
- Click "Calculate" to see the paintable area, the total area for all coats, the paint needed and the cost.
Formulas
With room length L, width W and wall height H, D doors and N windows, C coats and coverage c:
Door and window areas use typical sizes (1.6 m² and 1.2 m²). The final cost is always based on whole cans, because paint is sold in fixed sizes and you cannot buy a fraction of a liter.
Examples
- A room of 5 × 4 m with 2.7 m walls, 1 door, 2 windows, ceiling included, 2 coats, coverage 10 m²/L: walls = 2 × 9 × 2.7 = 48.6 m²; ceiling = 20 m²; deductions = 4 m²; paintable = 64.6 m²; total = 129.2 m²; paint = 13 L (≈ 3.4 gal). At 8 per liter, buying 13 L costs 104.
- The same room in feet (16 × 13 ft, 9 ft walls) with coverage 350 ft²/gal: walls = 2 × 29 × 9 = 522 ft²; ceiling = 208 ft²; deductions ≈ 43 ft²; paintable ≈ 687 ft²; total ≈ 1374 ft²; paint = 1374 ÷ 350 ≈ 4 gal (3.93 gal rounded up).
- A small bathroom of 2 × 2.5 m, 2.4 m walls, 1 door, 1 small window treated as 0, 2 coats, coverage 9 m²/L: walls = 21.6 m²; deductions 1.6 m²; paintable 20 m²; total 40 m²; paint = 4.4 L → buy 5 L.
Frequently asked questions
What coverage should I use?
Check the paint can. Most emulsions cover 8–12 m² per liter (350–450 ft² per gallon) on smooth interior walls. Use the lower end for rough plaster, bare drywall, textured surfaces or strong color changes, and the higher end for smooth, previously painted walls.
How do I treat very large or very small doors and windows?
The calculator subtracts fixed typical areas. For a double door, enter it as two doors; for small bathroom windows, reduce the window count. You can also measure the openings and add their area mentally.
Should I count a primer as a coat?
Primer usually has similar or slightly better coverage than paint, and it is a different product. Calculate the primer separately with the same area but the primer's coverage, then calculate the top coats.
How much extra paint should I buy?
The coats multiplier and whole-can rounding already provide a small margin. Keep any leftover paint for touch-ups; store it sealed and away from frost.
Does this include trim, skirting and ceilings other than flat ones?
No. The calculator handles flat walls and an optional flat ceiling. Trim, skirting boards, railings and textured ceilings need separate estimates — measure their length and use the trim paint's coverage per meter or foot of length.
Can I use feet for the room and metric coverage?
Yes. Choose the coverage unit independently of the room units; the calculator converts everything internally, so any combination works.
Is my data saved or sent anywhere?
No. Every calculation runs in your browser, and nothing you type is stored or sent to a server.
Related calculators
Other free calculators commonly used with this tool: Tile Calculator, Concrete Calculator, and Irregular Surface Area Calculator.
Want a deeper walkthrough? Read our paint quantity guide.