Paint Calculator for Two Coats

Running out of paint mid wall is a special kind of misery. This free paint calculator for two coats turns your walls into a shopping list: net wall area after doors and windows, total area across both coats, and the gallons or litres that covers at real world coverage rates. Add your price per tin and it prices the whole job too.

Last updated: October 22, 2026

Written by Ateeq Fareedi · Last updated October 22, 2026

The formula

Net wall area = (wall length × wall height) − openings
Total paint area = net wall area × number of coats
Gallons needed = total paint area ÷ coverage per gallon, rounded up

A worked example

A room with 60 ft of wall length at 8 ft high, less 40 sq ft for doors and windows, has 440 sq ft of net wall. Two coats means 880 sq ft of paint area, which needs 3 gallons at 350 sq ft coverage per gallon, about 11.3 litres, and comes to roughly $105 at $35 a gallon.

More about the Paint Calculator

How paint coverage math works

A complete example. A room with 60 ft of total wall length at 8 ft high: 480 sq ft of wall. Subtract 40 sq ft for doors and windows → 440 sq ft of net wall. Two coats (standard for a colour change) → 880 sq ft of paint area. At 350 sq ft per gallon that is 2.5 gallons, rounded up to 3, about 11.3 litres. At $35 a gallon, the paint bill is roughly $105. That is the entire job, priced, before you leave for the store.

The situations: a colour change repaint (two coats, the classic), a same colour refresh (one coat usually does it), a new build room on bare drywall (prime first, then two coats, the primer is non negotiable), and the feature wall (measure that one wall alone; a single wall rarely needs more than a gallon for two coats). Landlords repainting between tenants live by the one coat refresh; everyone else should plan for two.

Texture, waste and buying the right tins

Tips that save real money. Buy 10% more than the calculation says, touch ups, spilled trays and the wall you missed always consume it, and matching the colour later is a gamble. Keep the tin's coverage figure, not the generic 350, if your paint states its own. Paint in daylight so you see missed patches. And do the ceiling first if you are doing it: drips on fresh walls are heartbreaking.

What the calculator assumes: standard mid sheen wall paint at 350 sq ft per gallon, rectangular walls, honest measurements. Heavily textured walls can need up to 20% more; spray application uses more than rolling; and deep reds and yellows are notorious for needing a third coat regardless of what the maths says. Treat the result as a precise estimate, then add the 10% buffer and round up to tin sizes.

A room with a ceiling, worked end to end

Take a room 12 feet by 10 feet with 9 foot ceilings. The walls total 44 feet of length, so gross wall area is 44 times 9, 396 square feet. Subtract two doors at about 21 square feet each and a 15 square foot window, and net wall area is 339 square feet. Two coats means 678 square feet of painting, needing 1.94 gallons at 350 square feet per gallon, so buy 2 gallons.

The ceiling is a separate line, not an afterthought. It measures 12 times 10, 120 square feet, and two coats mean 240 square feet of coverage, or 0.69 of a gallon, so one gallon tin. Buy it as ceiling paint, formulated flatter to hide flaws under raking light, rather than using leftover wall paint. At $38 a gallon for wall paint and $30 for the ceiling tin, the room’s paint comes to $106.

Sheen, and the floor area mistake

Sheen changes how a room behaves more than how much paint you buy. Flat paint hides imperfections and suits bedrooms and ceilings, but marks easily and resists wiping. Eggshell and satin carry a slight shine that shrugs off cleaning, right for hallways and kitchens, but shows every bump beneath it. Coverage per gallon is broadly similar across sheens; the real cost of a glossier finish is the surface preparation it demands.

The most expensive measuring mistake is using floor area as wall area. This room’s floor is 120 square feet, which sounds like a gallon and a half of work, while its walls need 339 square feet per coat, nearly three times as much. Anyone who has run dry two thirds along the final wall has usually made this slip. Measure the walls themselves: length around the room, times ceiling height, minus doors and windows.

How to use the Paint Calculator

Add up the length of every wall you're painting, the room's perimeter works for a plain rectangle.
Enter the wall height and the combined area of doors and windows you won't be painting.
Set the number of coats: two for a colour change, one for a same colour refresh.
Keep coverage at 350 sq ft per gallon for a mid sheen wall paint unless your tin says otherwise, then press Calculate.

Frequently asked questions

How far does one gallon actually go?

Most wall paints stretch 350 to 400 sq ft per gallon in one coat over primed drywall. But texture drinks more, bare surfaces drink more, and deep colours over pale walls drink more too. Check the coverage printed on your actual tin, budget paint and premium paint are not the same product.

Do I need primer, and does it change the maths?

On new drywall, patches, bare wood or big colour jumps: yes. Primer seals the surface so the topcoat covers properly, and it can save you a whole finish coat, often cheaper than the extra paint would be. Budget primer at roughly paint like coverage, about 350 sq ft per gallon on fresh surfaces.

Is two coats really twice the paint of one?

Roughly, yes, the second coat covers the same area all over again. On bare or unprimed walls the first coat soaks in more, so allow a little extra for new surfaces. And a same colour refresh genuinely needs only one careful coat.

Do textured or rough walls really need more paint?

They do, every bump and crevice adds surface area, and heavily textured walls can need noticeably more paint than smooth drywall, sometimes around a fifth extra. If your walls have knockdown, orange peel or heavy texture, set your coverage figure a little lower in the calculator above to be safe. A tester pot on your actual wall is the honest way to check.

How much paint do I need for a room?

Calculate total wall area (length × height for each wall), subtract about 20 sq ft per door and 15 sq ft per window, then divide by 350 sq ft per gallon. A 12×12 room with 8-ft ceilings needs about (384 − 60) ÷ 350 ≈ 1 gallon per coat, buy 2 gallons for two coats plus touch-ups.

Should doors and windows be subtracted in the paint calculation?

Yes, always. Measure the width and height of each door and window, calculate their area, and subtract it from the total wall area before dividing by the coverage stated on the can. This simple step avoids buying an extra can and wasting money.

How many coats of paint are needed for a good finish?

For most interior walls two coats are needed to cover the previous color well and get an even finish. Porous surfaces or low coverage paints may need a third coat. In Brazil, plan on roughly 5 to 6 m² per liter per coat for most latex wall paints.

How do I calculate paint for exterior walls of a house?

Work wall by wall, just as you would indoors: multiply each wall’s width by its height up to the eaves, add the four results, and subtract the doors and windows. A gable end is a rectangle plus a triangle, the triangle’s area is half its base times its height. Exterior surfaces usually drink more paint than smooth interior plaster, especially render, brick and weatherboard, so enter a lower coverage figure than the tin’s most optimistic number and keep the calculator’s two coat assumption.

How do I work out paint for a room with a sloped or vaulted ceiling?

Split the room into simple shapes. The walls under the slope are measured normally, and each sloping end wall is a rectangle up to where the slope starts, plus a triangle above it, the triangle’s area is half the wall’s width times the extra height at the peak. If the sloped ceiling itself is being painted, measure along the slope rather than across the floor: a room 12 feet wide with a slope length of 9 feet has 108 square feet of sloped ceiling on that side.

Does the paint calculator give litres for the UK, Canada and Australia?

Yes. It shows the US gallons needed and the same amount in litres. Paint in Australia and the UK is sold in litre tins, so use the litres figure and round up to the next tin size.

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