Paint Calculator
Estimate how many gallons of paint are needed for room walls based on dimensions, coats, and coverage rate.
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Paint Calculator: how it works
Practical information to understand the result and use this tool correctly.
About Paint Calculator
This paint coverage calculator turns wall measurements into liters and whole cans. It is for planning a purchase, not for a contractor quote.
Net area is wall length times height, minus door and window openings. Paintable area multiplies that net area by the number of coats and by a waste factor. Liters are paintable area divided by the coverage printed on the can, in square meters per liter.
Use it when the label gives coverage (often 8–12 m²/L for interior latex) and you need to know whether a 4 L or 10 L can is enough. Optional price per liter estimates material cost only.
It does not account for textured walls, dark-to-light color changes, porous masonry, or primer plus finish as separate products unless you run the calculator twice. Coverage on the label is a lab figure; rough surfaces can use 20–40% more.
How to use it
- 1Enter total wall length and height in meters, then subtract openings in square meters.
- 2Pick a preset or set coats, coverage in m² per liter, waste, and can size.
- 3Optionally add price per liter to see a material estimate.
- 4Read liters, cans to buy, and leftover paint. Round up to whole cans.
- 5Copy the result or reset and try another finish.
Frequently asked questions
- How are paint liters calculated?
- Net area is length × height − openings. Paintable area is net area × coats × (1 + waste/100). Liters are paintable area divided by coverage in m² per liter. Cans are liters divided by can size, rounded up.
- What coverage should I enter?
- Use the figure on the can, usually m² per liter or per coat. Interior latex is often around 10 m²/L, primer a bit higher, exterior masonry lower. If the label is per gallon, convert first (1 US gallon ≈ 3.785 L).
- Does waste include cutting in and a second coat?
- Coats are a separate input. Waste covers offcuts, tray residue, and uneven suction. A typical allowance is 10% on smooth walls and 15% outside or on new plaster.
- Is the room measurement uploaded?
- No. The calculation stays in the browser and nothing is sent to a server.
- How is this different from a paint cost multiplier?
- A simple area × price tool does not split liters from can size or subtract openings. This calculator does both, and price is optional.