Practical tools for measured work
Paint Calculator
Calculate how much paint you need for walls, accounting for doors, windows and coats.
How it works
How to use it: enter your total wall length (add up every wall you're painting, since the tool works on total run), the wall height, the combined area of doors and windows to exclude, how many coats you're applying, and the coverage rate printed on the paint can.
Formula. The tool multiplies wall length by height for the gross area, subtracts the openings area, then scales by the number of coats and divides by coverage per litre:
Paintable area = length × height − openings and Paint needed (L) = paintable area × coats ÷ coverage
Worked example. With the defaults above (12 m of wall, 2.4 m high, 4 m² of openings, 2 coats, 10 m²/L coverage): gross area = 12 × 2.4 = 28.8 m²; paintable area = 28.8 − 4 = 24.8 m²; paint needed = 24.8 × 2 ÷ 10 = 4.96 L, which converts to 4.96 ÷ 3.78541 ≈ 1.31 US gallons.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- Total wall length
- 12 m
- Wall height
- 2.4 m
- Doors/windows area
- 4 m2
- Coats
- 2
- Coverage per litre
- 10 m2/L
Primary result: Paint: 4.96 L.
Before using the result
- Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
- Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
- When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.
Limitations
The 10 m²/L coverage default is a rough midpoint - actual coverage varies widely by paint type (emulsion vs. gloss), surface porosity, application method (roller vs. spray), and colour change (a light-over-dark repaint often needs an extra coat). Always check the coverage rate stated on your specific product.
The calculator treats openings as a single subtracted area and does not add extra paint for trim, ceilings, texture, or a spare-can buffer - round up and buy a little extra, especially for custom-mixed colours that are hard to rematch exactly.
Frequently asked questions
Should I round up the litres I buy?
Yes. Paint is sold in fixed can sizes, coverage figures are averages, and it's far cheaper to have a little leftover than to run out mid-wall and have to colour-match a new batch. Round up to the next can size.
Do I need to subtract the ceiling or floor area?
No - this tool only calculates wall area (length × height), so ceilings and floors are already excluded. Only the doors, windows, and other openings you enter are subtracted from the wall area.
Why does a second coat use almost as much paint as the first?
The formula multiplies paintable area by the number of coats directly, since each full coat covers the same area. Some painters use noticeably less on a second coat over a well-sealed first coat - if that applies to you, raise the coverage rate rather than changing the coat count.
Related tools
Tile Layout Calculator
Plan a tile grid across a room, centered or edge-started, with grout gaps and edge-cut sizes.
Baluster Spacing Calculator
Enter the railing opening, baluster width and maximum gap you intend to use to calculate an equal-spacing layout.
Fence Picket Spacing
Lay out fence picket spacing across a run, with a live diagram of the finished fence section.
Stair Calculator
Work out riser and tread count, riser height and stair angle from total rise and run.