Paint Calculator
Calculate how much paint you need for a room from its wall size, coats, and coverage rate — free and instant.
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.
Doors and windows are excluded as one combined area, not calculated individually.
Estimated cost is 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
How much paint you actually need
The question "how much paint do I need" comes down to one calculation, repeated with the right numbers: total area to paint, divided by how much area your paint covers per liter or gallon. This calculator does exactly that, with two adjustments that matter in practice — accounting for multiple coats, and excluding the doors and windows you are not painting.
The calculation, step by step
- Gross wall area = wall width × wall height × number of walls
- Net wall area = gross area − doors/windows excluded
- Total area to cover = net area × number of coats
- Paint needed = total area to cover ÷ coverage rate
The reason coats matter so much: painting a wall twice does not use twice the *wall* area, but it does use twice the *paint*, because you are covering the same surface a second time. A room that needs 4 liters for one coat needs roughly 8 liters for the two coats most painters recommend for full, even color coverage.
Why coverage rate is a range, not a fact
Paint coverage is usually printed on the can as a range — something like "350–400 sq ft per gallon" — and the real figure for your specific wall depends on:
| Factor | Effect on coverage |
|---|---|
| Surface porosity | A porous or unprimed wall absorbs more paint, reducing coverage |
| Paint sheen/type | Flat paints often spread further than glossier finishes |
| Application method | Spraying uses more paint than rolling for the same visual result |
| Color change | Painting a dark wall a light color often needs an extra coat regardless of "coverage rate" |
This calculator's default (10 m²/liter, or 350 sq ft/gallon) is a reasonable starting estimate for typical interior wall paint, not a measurement of your specific product. Always check the coverage figure printed on your actual paint can and enter that instead — it is the only number that reflects the paint you are actually using.
How many coats do you really need
Two coats is the standard recommendation for most interior painting projects, and this calculator defaults to it. There are real exceptions in both directions:
- One coat is sometimes enough when the new color closely matches the old one and the wall is already primed and in good condition.
- Three coats are common when painting a light color over a dark one, or a saturated color (reds, deep blues) that needs extra coverage to look even and opaque.
If you are unsure, budget for two coats and buy the paint in one trip — running out mid-project and needing a second can from a different batch risks a visible tone difference, the same batch-matching problem that applies to tiles and other finish materials.
Excluding doors and windows
This calculator subtracts a single combined area for every door and window in the room, rather than requiring you to enter each one individually. A standard interior door is roughly 1.6–2 m² (about 18–21 sq ft), and a typical window varies more widely, from under 1 m² to several square meters for a large picture window. For a quick estimate, adding up the doors and windows in the room (or simply leaving this at zero for a deliberately generous, worst-case estimate) both work — the exclusion mainly matters when a room has an unusually large amount of glazing or several doors, where skipping it would meaningfully overestimate how much paint you need.
What this calculator does not account for
- Ceilings. This is a wall-only calculator. If you are painting the ceiling too, calculate its area separately at the same coverage rate.
- Textured or masonry surfaces. Stucco, brick, and heavily textured walls absorb significantly more paint than smooth drywall — increase your estimate accordingly, or better, check the paint manufacturer's guidance for textured surfaces specifically.
- Primer. A separate coat of primer, when needed, uses its own quantity of primer at (usually) its own coverage rate — this calculator only estimates the topcoat paint.
- Waste from cutting-in, spills, and touch-ups. Professional painters often buy slightly more than the strict calculation to cover edge work with a brush and inevitable touch-ups later.
Measure your walls, check your specific paint's coverage rate on the can, and round up rather than down. Everything here is computed in your browser; nothing you enter is sent anywhere.
FAQ
How much paint do I need for a room?
Multiply your wall area by the number of coats, then divide by your paint's coverage rate. This calculator does all of that — enter the wall dimensions, number of walls, coats, and coverage rate, and it returns liters or gallons needed.
Where do I find the real coverage rate for my paint?
On the can or tin — manufacturers print a coverage range (e.g. "350–400 sq ft per gallon") specific to that product. The default in this calculator (10 m²/liter, or 350 sq ft/gallon) is a commonly cited average, not a measurement of your specific paint, so use the printed figure when you have it.
Why does painting twice not double the wall area, but does double the paint?
The wall you are painting stays the same size regardless of how many times you paint it — but each additional coat covers that same area again, which uses roughly the same amount of paint as the first coat did. Two coats typically means roughly double the paint of one coat.
Do I need one coat, two coats, or three?
Two coats is the standard recommendation for most projects and full, even coverage. One coat can be enough when the new color closely matches the old one on an already-primed wall. Three coats are common when covering a dark color with a light one, or when using a saturated color that needs extra coverage.
How do I account for doors and windows?
Enter their combined area in the "Doors & windows to exclude" field. A standard interior door is roughly 1.6–2 m² (18–21 sq ft); windows vary more. Leaving this at zero gives a deliberately generous, worst-case estimate, which is a reasonable choice for a small room with few openings.
Does this include the ceiling?
No — this calculator is walls only. If you are painting the ceiling too, calculate its area (length × width) separately using the same coverage rate.
Does this include primer?
No. This estimates the topcoat paint only. Primer, when needed, is a separate product with its own coverage rate and should be calculated separately.
What about textured walls, brick, or stucco?
Textured and masonry surfaces absorb noticeably more paint than smooth drywall, so this calculator's estimate will run low for them. Check your paint manufacturer's specific guidance for textured surfaces, or increase your estimate as a safety margin.
Can I get a cost estimate, not just a quantity?
Yes, optionally. Enter your price per liter (or per gallon in US units) and the calculator adds an estimated total cost. Leave it at zero to skip this — the cost covers paint only, not primer, brushes, tape, or labor.
Should I round up the amount I buy?
Yes. Paint is sold in fixed container sizes, running out mid-wall creates a visible seam if you switch to a different batch, and most estimates (including this one) do not include a margin for spills, cutting-in with a brush, or future touch-ups.