Paint Calculator
Calculate how much paint — and primer, if you need it — a room takes from its wall size, coats, and coverage rate. Free and instant.
Advanced options
Use the size sold by your supplier; zero skips can rounding.
Your result
Updates as you type- Paint needed
- 7.68 L
- Cans to buy
- 2
- Net wall area
- 38.4 m²
Covers 38.4 m² of wall at 2 coats.
Whole cans of 5 L.
Wall area after excluding doors and windows.
More result details
Method, assumptions, and tips
Room mode uses 2 × (length + depth) × height, plus optional ceiling area. Whole-can rounding applies to finish paint; primer and labor costs are separate.
Assumes flat rectangular walls with no allowance for texture, which increases how much paint a surface absorbs.
The default coverage rate (10 m²/liter, or 350 sq ft/gallon) is a commonly cited industry figure, not a measurement of your specific paint — real coverage typically ranges 8–12 m²/liter (250–400 sq ft/gallon) depending on the product and surface porosity.
Individual door and window measurements are added to any additional excluded area. Enter each deduction once.
Estimated cost is topcoat paint only — it excludes primer, brushes, rollers, tape, and labor.
We multiply the wall area by your number of coats, then divide by how much area one liter (or gallon) of your specific paint covers.
Coverage rate varies a lot by product and surface — check the can or tin for the manufacturer's stated rate rather than trusting the default here.
Estimating how much paint to buy for a straightforward room before a trip to the hardware store.
How it works
Start with the surfaces you will paint
Use equal-wall mode when you have several walls with the same dimensions. Use rectangular-room mode when you know the room’s length, depth and wall height. In room mode the wall area is 2 × (length + depth) × height. Include ceiling adds length × depth using the same coats and coverage settings.
If the ceiling uses a different paint or a different number of coats, estimate it separately. For an irregular room, measure its surfaces in sections; a bounding rectangle can overstate the area.
A room estimate, checked step by step
Load “4 × 3 m room: paint + primer” above. The room dimensions, coverage rates and prices are illustrative. Replace them with your measurements and product details before using the estimate to shop.
| Setting | Example input |
|---|---|
| Room length × depth × height | 4 m × 3 m × 2.5 m |
| Ceiling | Included |
| Door | One, 1 m × 2 m |
| Window | One, 1 m × 1 m |
| Finish paint | Two coats, 10 m²/L per coat |
| Finish can size and price | 5 L, $10 per litre |
| Primer | One coat, 7.5 m²/L |
The arithmetic is:
- Walls:
2 × (4 + 3) × 2.5 = 35 m². - Ceiling:
4 × 3 = 12 m². - Openings:
1 × 2 + 1 × 1 = 3 m². - Net surface:
35 + 12 − 3 = 44 m². - Finish paint:
44 × 2 ÷ 10 = 8.8 L. - Whole 5 L cans: round
8.8 ÷ 5up to 2 cans, giving 10 L purchased. - Primer, separately:
44 × 1 ÷ 7.5 = 5.87 Lto two decimal places.
At the entered price, finish paint costs $88 before can rounding and $100 for the whole cans purchased. The cost does not include primer, tools or labour. The primer result is a quantity estimate; the tool does not round it to primer cans or include it in the finish-paint purchase cost.
Compare coats and ceiling before buying
Keep the same 4 × 3 × 2.5 m room and 3 m² of openings. At an illustrative 10 m²/L for finish paint, these are four separate estimates:
| Ceiling | Finish coats | Net surface | Finish paint | Whole 5 L cans | One primer coat at 7.5 m²/L |
|---|---|---|---|---|---|
| Excluded | 1 | 32 m² | 3.2 L | 1 | 4.27 L |
| Excluded | 2 | 32 m² | 6.4 L | 2 | 4.27 L |
| Included | 1 | 44 m² | 4.4 L | 1 | 5.87 L |
| Included | 2 | 44 m² | 8.8 L | 2 | 5.87 L |
Load the room example, then change Include ceiling and Number of coats to reproduce the rows. Primer stays at one coat in this comparison; increasing finish coats does not increase primer quantity. The ceiling contributes 12 m² per coat. These scenarios compare quantities, not recommended coat counts: follow your product instructions. Estimate a ceiling separately when its paint or coverage differs.
Coverage is an input, not a universal constant
Use the coverage stated for your actual product and surface. A rate of 10 m²/L means one litre covers ten square metres for one coat under the assumed conditions. It does not mean a ten-square-metre wall needs one litre for the whole job when two coats are specified.
Finish paint and primer have separate coverage settings. Selecting primer does not replace a finish coat or change the finish-paint quantity. Whether a surface needs primer, and how many coats to apply, should come from the product instructions and the surface’s condition. This calculator does not assess either.
Avoid subtracting an opening twice
Advanced options let you enter individual doors and windows and an additional area to exclude. The tool adds those deductions. If a two-square-metre door is already entered individually, do not include it again in the additional excluded area.
In the worked example, the net area should be 44 m². If it is smaller, check for a duplicate deduction or an unintended ceiling setting before changing the coverage rate.
Turn the estimate into an order
Use the package size sold by the supplier. Whole-can rounding is separate from allowing for spills, edge work or future touch-ups: the leftover 1.2 L in this example comes from rounding the purchase, not from a modeled waste percentage. Check the product’s instructions before treating that remainder as sufficient allowance.
Keep the measurements and the coverage figures with your shopping list. If the estimate changes, those inputs tell you why. Use Tile Calculator for floor coverage; paint coverage rates cannot be used to estimate tiles.
FAQ
How much paint does the worked 4 × 3 m room need?
With a 2.5 m height, ceiling included, a 2 m² door and 1 m² window, the net area is 44 m². Two coats at 10 m²/L need 8.8 L: two whole 5 L cans.
How much primer does that room need?
One coat over 44 m² at 7.5 m²/L needs about 5.87 L. Primer quantity is separate from finish paint and is not included in finish-paint purchase cost.
Should I subtract doors through both controls?
No. Individual opening measurements and the additional excluded-area field are added together. Enter each surface deduction once.
Does the tool include the ceiling?
Rectangular-room mode can include it. It then uses the same coats and coverage as the walls. Estimate the ceiling separately if it uses a different product or coat count.
Does the estimate include waste or touch-up allowance?
There is no separate waste percentage. Whole-can rounding can leave extra paint, but does not assess whether that is enough for your job. Choose an allowance using your product and surface requirements.
Which coverage rate should I use?
Use the product’s stated coverage for the relevant surface and one coat. Finish paint and primer have separate rates. The defaults are assumptions, not measured coverage for your product.