Calculators
Interior paint calculators
How much wall, ceiling, trim, door and cabinet paint a room or a whole house takes.
Every interior estimate is the same three steps: measure the surface, subtract what you will not paint, and divide by what a gallon really covers. Walls are measured as perimeter times height with the doors and windows taken out; ceilings are length times width; trim and doors are small enough that the answer comes in quarts. These calculators do each of those sums in the open, with the coverage rate as an input you can change when the can says something different.
The defaults are a previously painted, smooth wall at two coats and 350 square feet per gallon per coat, which is the middle of what the big manufacturers print on their data sheets. Bare drywall, dark colours, textured walls and ceilings all drink more, and each calculator says where that extra comes from.
10 calculators
Wall Paint Calculator
Gallons and cans for the walls of a room from its size, openings, coats and coverage.
Ceiling Paint Calculator
Ceiling paint by room size and texture, from smooth to popcorn, rounded to cans.
Trim & Baseboard Paint Calculator
Quarts of trim enamel for baseboards, crown, door and window casings.
Door Paint Calculator
Paint for a set of doors by style, size, sides and coats.
Window Frame & Sash Paint Calculator
Quarts for window frames, casings and sashes by window size and count.
Accent Wall Paint Calculator
Paint, tinted primer and sample pots for one feature wall, with extra coats for dark colours.
Primer Calculator
Primer gallons by surface: new drywall, patches, colour changes, glossy or stained walls.
Whole-House Interior Paint Estimator
Wall, ceiling and trim paint for a whole house from a count of rooms by size, with optional prices.
Kitchen Cabinet Paint Calculator
Primer and enamel for cabinet doors, drawer fronts and face frames, brushed or sprayed.
Stairwell & Tall Wall Paint Calculator
Paint for up to four tall or sloping walls, with a warning when the height needs a scaffold.
Guides for this topic
Dark colours, LRV and the extra coats they cost
A navy wall can take half as much paint again as a pale one. The number on the back of the paint chip tells you before you buy, and a tinted primer is usually the way round it.
How many coats of paint you really need
The number of coats changes the order more than any other input. Here are the rules, the reasons behind them, and the cheaper way round a third coat.
How much paint do I need? The complete method
Five steps turn a tape measure and a paint can label into an order that will not run short, and a worked room shows each of them with real numbers.
Measuring a room for paint (and what to subtract)
Ten minutes with a tape measure is all a paint estimate needs, if you measure the right things and subtract only what is worth subtracting.
Paint coverage explained: why 400 sq ft a gallon rarely happens
The coverage on the can is a laboratory number. Here is what eats into it on a real wall, by how much, and which figure to plan with instead.
Painting a room: quantities, order of work and timing
Ceiling, walls, trim, in that order, and about two days of work for a bedroom. Here is the shopping list, the sequence and the hours, worked through for one real-sized room.
Painting kitchen cabinets: how much primer and paint, and why
A kitchen of cabinets is only about 180 sq ft of surface, but it is the hardest-wearing paint job in the house. The quantity is small; the prep and the product decide whether it lasts.
Primer: when you need it and when you can skip it
Primer is either essential or a waste of a day, depending on the surface. Here is how to tell which, which primer to buy, and how much.
Textured and popcorn ceilings: coverage, product and technique
A popcorn ceiling can take two thirds more paint than a smooth one of the same size. Here is why, how to plan for it, and how to paint it without pulling the texture down.
Trim, doors and windows: the quart maths
Trim is a small area and a lot of work. Here is how to turn linear feet and door counts into quarts, and why the answer is usually two or three quarts more than people think.
Two-tone and wainscot walls: proportions, paint and a sharp line
A colour split at a third of the wall height, darker below, is the classic. Here is how to choose the height, how much of each colour to buy, and how to get a line that is straight and sharp.
Wallpaper paste, prep and removal planning
The paper is the visible part of a wallpaper job. The primer under it, the right paste, and the hours of removal before it decide whether it goes up smoothly and comes down again in one piece.
Questions people ask
- How much paint do I need for a 10 × 10 room?
- With 8 ft ceilings, one door and one window, a 10 × 10 room has 320 sq ft of wall minus 35 sq ft of openings, so 285 sq ft to paint. Two coats at 350 sq ft per gallon is 1.63 gallons, and with a 5% allowance 1.71 gallons: buy one gallon and three quarts, or two gallons if you want some left for touch-ups. The ceiling is another 100 sq ft, about a quart and a half per coat.
- Can I use the same paint on the walls and the ceiling?
- You can, but flat ceiling paint hides roller marks and spatters less, and it is usually cheaper. Ceilings also take a slightly different quantity: a smooth ceiling covers at 350 to 400 sq ft per gallon, a popcorn ceiling at 200 to 250 because the texture roughly doubles the surface area.
- Do I subtract doors and windows?
- Yes. A standard 36 × 80 in door is 20 sq ft and a typical window about 15 sq ft, and the calculators take those out of the wall area. Openings under about 10 sq ft are not worth subtracting; the paint saved is less than the rounding to the next can.
- How much paint does a whole house interior take?
- It depends on the rooms more than on the floor area. The whole-house estimator counts rooms by size, adds hallways, ceilings and trim, and reports each product separately, because wall paint, ceiling paint and trim enamel are bought in different cans. A typical three-bedroom house at two coats lands somewhere between ten and twenty gallons of wall paint.
- How many rooms does one gallon cover?
- At 350 sq ft per coat, one gallon covers the walls of a 10 × 10 room once, with a little left. It will not cover two coats of anything larger than a small bathroom. Two coats is the normal job, so a gallon is a one-room-at-a-time quantity, and only for small rooms.
More calculators on our other sites
Floorings Calculator
How much tile, wood, vinyl, carpet, underlayment and trim a floor needs, and what it costs.
Roofings Calculator
Shingles, pitch, rafters, metal panels, gutters, ventilation and what a new roof costs.
The Woven Garden
Garden and yard calculators for mulch, soil, gravel, sod, pavers, fences and decks.