What about doors and windows?
This estimates total wall area. Subtract roughly 1.5-2 sq m per door and 1 sq m per window if needed.
Lifestyle
Paint Calculator
Enter the room perimeter, wall height, and number of coats to calculate the total paint needed in gallons or liters.
Live calculator output
Enter room dimensions and coats to see the paint estimate.
How it works
The calculator multiplies the room perimeter by the wall height to get total wall area, then multiplies by the number of coats. The formula is: Liters = (Perimeter × Height × Coats) ÷ Coverage per Liter.
Paint is also shown in gallons (1 gallon = 3.785 liters). This gives you a reliable shopping estimate, though you may want to subtract area for large doors and windows.
Practical example
A room with a 16 m perimeter and 2.5 m walls has 40 sq m of wall area. With 2 coats: (16 × 2.5 × 2) ÷ 10 = 8 liters (about 2.1 gallons).
A standard gallon of paint covers about 37–40 sq m, so you would buy 3 gallons to be safe. Always round up — running out mid-coat causes visible inconsistencies.
Frequently asked questions
How many coats do I need?
Two coats is standard for most paints. Dark to light color changes may need three.
What is typical coverage per liter?
Most interior paints cover 8-12 square meters per liter. Check your paint label for specifics.
Should I use a primer?
Yes, for new drywall, dark-to-light color changes, or stained surfaces. Primer improves adhesion and reduces the number of topcoats needed.
How do I measure the room perimeter?
Measure each wall length and add them together. For a 4m × 4m room, the perimeter is 16m. For an L-shaped room, measure all wall segments.
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