Paint Coverage Calculator
Calculate the exact litres of paint needed for any room, wall, or exterior surface.
📖 What is a Paint Coverage Calculator?
A paint coverage calculator tells you exactly how many litres of paint you need to cover a given area. Whether you're repainting a room, an exterior wall, or a fence, buying the right amount of paint upfront saves money and ensures colour consistency - since different production batches of the same colour can have slight variations.
Calculating paint quantity requires knowing the total paintable area, the coverage rate of your chosen paint (in m² per litre), and the number of coats you plan to apply. This calculator handles room painting automatically - it calculates all four walls' area and subtracts standard door and window areas.
The coverage rate printed on a paint tin is measured under ideal conditions on smooth surfaces. In practice, coverage is lower on rough, porous, or dark surfaces that require more product to achieve opacity.
📐 Formula
Wall Area = 2 × (Length + Width) × Height
Deductions = (No. of Doors × 1.6) + (No. of Windows × 1.2)
Net Paintable Area = Wall Area − Deductions
Paint per Coat = Net Area / Coverage Rate (m²/L)
Total Paint = Paint per Coat × Number of Coats
Buy Quantity = Total × 1.10 (add 10% buffer)
📖 How to Use This Calculator
1
Select Room (all 4 walls) or Single Wall mode.
2
Enter dimensions and the number of doors and windows.
3
Set coverage rate (check the paint tin - typically 10-14 m²/L) and number of coats (default 2).
4
Click Calculate to get total paint needed and recommended buy quantity.
💡 Example Calculations
Example 1 - Living room
1
5m × 4m room, 3m ceiling, 1 door, 2 windows. Coverage 12 m²/L, 2 coats.
2
Wall area = 2 × (5+4) × 3 = 54 m²
3
Deductions = 1.6 + 2.4 = 4.0 m²
4
Net area = 50 m²
5
Paint per coat = 50/12 = 4.17 L
6
Total (2 coats) = 8.33 L → Buy 9.2 L with 10% buffer
Example 2 - Single exterior wall
1
8m × 3m wall, no openings, coverage 10 m²/L (exterior paint), 2 coats.
2
Area = 24 m²
3
Total = 24/10 × 2 = 4.8 L → Buy 5.3 L
Frequently Asked Questions
How much area does 1 litre of paint cover?
Coverage depends on the paint type and surface. Standard interior emulsion covers 10-14 m² per litre per coat on smooth walls. Exterior paint covers 8-12 m² per litre. Premium paints may cover up to 16 m² per litre on smooth surfaces.
How many coats of paint do I need?
Typically 2 coats for a smooth finish on a previously painted wall. If painting over a dark colour with a light one, or on a bare surface, 3 coats may be needed. A primer coat before painting new walls improves coverage and reduces the number of topcoats needed.
Should I paint the ceiling separately?
Yes - ceiling paint is usually a flat white and often a different product from wall paint. Calculate ceiling area (length × width) separately. Most ceilings need 2 coats of ceiling paint.
Do doors and windows reduce the paint area?
Yes, significantly. A standard interior door is approximately 2m × 0.8m = 1.6 m². A standard window is approximately 1.2m × 1m = 1.2 m². This calculator subtracts these automatically based on the number of doors and windows you enter.
What is the difference between interior and exterior paint?
Exterior paint contains additional UV stabilisers, fungicides, and is more durable against weather. Interior paint prioritises washability and low VOC (volatile organic compound) content. Never use interior paint outside - it will fade and peel.
How many coats of paint does a wall need?
Most interior walls need 2 coats of finish paint for complete, even coverage. New walls (freshly plastered or bare drywall) need a primer coat first, then 2 finish coats (3 total applications). Dark colours being painted over a lighter colour, or light colours over dark, may need 3 finish coats. Exterior walls typically need 2 coats of exterior paint every 5-7 years. High-quality paints with better coverage may achieve full opacity in 2 coats without primer on previously painted surfaces.
What is the coverage per litre of interior wall paint?
Standard interior emulsion (latex) paint covers approximately 10-14 square metres per litre per coat. Premium paints with better pigment density may cover 12-16 m^2/L. Textured paints and masonry paints cover less (8-10 m^2/L) due to surface absorption. Always check the manufacturer's stated coverage on the tin and divide by 1.1-1.2 for practical real-world coverage (accounting for surface roughness and application losses).
How do I calculate how much paint I need for a room?
Measure the perimeter of the room and multiply by the ceiling height to get total wall area. Subtract roughly 2 m² per door and 1.5 m² per window. Divide the net area by your paint's coverage rate (typically 10-12 m²/L) to get litres needed per coat, then multiply by the number of coats. Add 10% for waste and touch-ups. This calculator does all of this for you - enter room dimensions, door/window counts, coverage rate, and number of coats.
How many coats of paint do I need and how does it affect the quantity?
Interior walls typically need 1 primer coat plus 2 finish coats. Exterior surfaces may need 1-2 primer coats plus 2 topcoats for weather protection. Each coat uses roughly the same amount of paint. This calculator lets you set the number of coats - the total paint required scales linearly with the coat count.