Paint Calculator
How many gallons or quarts a room, a ceiling or a house needs, with doors, windows and coats counted.
Works in your browser. Nothing you type is sent to us.
Type 12' 6" or 12.5 for twelve and a half feet. Measure the height from the floor to the ceiling.
Take away
Each door takes away 21 sq ft (3 by 7 feet) and each window 15 sq ft (3 by 5 feet).
Paint
The can gives the coverage, usually 350 to 400 sq ft per gallon on a smooth wall. Use a lower number for rough, porous or new surfaces.
The working
| Surface | Working | sq ft |
|---|
Trim, doors and window frames are not included; a quart usually does the trim of one room. Worked out in your browser. Nothing you type is sent to us.
Paint Calculator at a glance
- Price
- Free
- Data sent to us
- None, it runs in your browser
- Sign-up
- Not needed
- Measures
- Feet and inches, or metres
- Gives
- Area, gallons or litres, cans to buy, cost
- Default coverage
- 350 sq ft per gallon, change it to your can's
How to use Paint Calculator
- MeasureType the room's length, width and wall height, or choose Wall by wall and type each wall.
- Take away openingsType the number of doors and windows.
- Choose coatsPick the number of coats and type the coverage from the can. Tick primer if you need it.
- Read what to buyThe cans to buy, the exact amount and the working appear at once.
Type the length, width and wall height of a room, or each wall one by one for the outside of a house, then the number of doors and windows and how many coats. The calculator gives the area to paint, the paint needed and what to buy in five-gallon buckets, gallons and quarts, or litre tins in metric, with an optional coat of primer and a cost. The working is shown line by line so you can check it.
How it works
Paint Calculator is a web page that does its work on your own device. Everything you type or choose is worked out by your browser and never sent to a server, so nothing is stored and there is nothing to delete. There is no account, no sign-up and no limit on how often you use it.
Straight to one job
Exterior Paint Calculator · Ceiling Paint Calculator
How the paint is worked out
For a room, the wall area is the distance around the room times the height: a room 12 feet by 12 feet with 8-foot walls has 2 × (12 + 12) × 8 = 384 square feet of wall. Each door takes away about 21 square feet and each window about 15, so one door and two windows leave 333 square feet. Two coats double that to 666 square feet, and at 350 square feet a gallon that is 1.9 gallons, so you buy 2 gallons. The ceiling, if you paint it, is the length times the width.
For the outside of a house, a stairwell or walls of different heights, choose Wall by wall and type each wall as its width and height. For a gable end, the triangle above the eaves is half the width times the height of the peak; add it as a wall of that area, or as a wall half as wide.
Coverage and coats
The coverage printed on the can is for a smooth, primed wall. Textured walls, bare plaster, new drywall, rough siding and brick soak up more, so type a lower number, such as 250 to 300 square feet a gallon. Two coats is the usual advice for an even colour; a big change of colour, especially light over dark, may need a third coat or a tinted primer first.
| Surface | Typical coverage per gallon |
|---|---|
| Smooth, primed interior wall | 350 to 400 sq ft |
| Textured wall or ceiling | 250 to 350 sq ft |
| New drywall, with primer | Primer 200 to 300 sq ft, then paint as above |
| Rough siding, stucco, brick | 200 to 300 sq ft |
These are typical ranges; the label on your can is the figure to trust.
Buying paint
Paint comes in quarts, gallons and five-gallon buckets. The calculator rounds up to whole containers and turns three quarts into a gallon, since a gallon usually costs about the same. If you need several gallons of one colour, ask the store to mix them together, or pour them into one bucket before you start, so a slight difference between cans does not show on the wall. Keep the leftover, labelled with the room, for touch-ups.
What it does
- A room from its length, width and height, or wall by wall
- Walls, ceiling or both
- Doors and windows taken away
- One, two or three coats, with your can's coverage
- Buckets, gallons and quarts to buy, or litre tins
- Optional primer coat and cost
- Feet and inches or metres
Questions
How much paint do I need for a 12 by 12 room?
With 8-foot walls, one door and two windows, there are about 333 square feet of wall. Two coats at 350 square feet a gallon need 1.9 gallons, so buy 2 gallons. Painting the ceiling as well adds 144 square feet a coat, about another gallon for two coats.
How many square feet does a gallon of paint cover?
Most interior paints say 350 to 400 square feet a gallon on a smooth, primed wall. Rough, textured or porous surfaces take more paint, so allow 250 to 300 square feet a gallon there. The figure on your can is the one to use.
How do I calculate the wall area of a room?
Add the length and width, double it to get the distance around the room, and multiply by the wall height. Then take away about 21 square feet for each door and 15 for each window.
Do I need two coats of paint?
Usually, yes. One coat often looks patchy, especially over a different colour. Two coats give an even finish; a dark colour over a light one, or the other way round, may need a primer or a third coat.
How much primer do I need?
One coat over the same area. Primer usually covers 200 to 300 square feet a gallon, less than paint, because it soaks into bare surfaces. Tick Add one coat of primer and type the coverage from its can.
How much paint do I need for the outside of a house?
Choose Wall by wall and type each side of the house as its width and height, plus the doors and windows. Rough siding and stucco take more paint, so use a lower coverage, such as 250 to 300 square feet a gallon.
Is anything sent anywhere?
No. The sums run in your browser and nothing you type is sent to us or stored.
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