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FREE CALCULATOR
Paint Coverage Calculator
Work out how much paint you need for a room or a wall. Enter the size, doors, windows and coats, and get the paint needed in gallons or litres, plus a simple amount to buy.
Enter the size of your room or wall and press Calculate to see how much paint to buy.
What Is a Paint Coverage Calculator?
A paint coverage calculator tells you how much paint to buy for a room or a wall. You enter the size of the space, take away the doors and windows, choose the number of coats and add the coverage printed on your paint can. The calculator does the rest and shows the paint you need in gallons or litres.
Buying the right amount saves money and avoids a second trip to the store. It also helps you finish the job with paint from the same batch, so the colour looks the same on every wall.
How to Use This Paint Calculator
- Choose the units. Pick feet and gallons, or metres and litres.
- Pick whole room or single wall. For a room, enter length, width and ceiling height. For one wall, enter its width and height.
- Add doors and windows. They are deducted from the wall area so you do not buy paint you will not use.
- Set the coats and extra paint. Two coats and 10% extra is a safe choice for most rooms.
- Enter the paint coverage. Copy it from the paint can. The default is 350 sq ft per gallon.
- Press Calculate. See the paint needed and a simple amount to buy.
How Much Paint Do You Need?
The calculator uses a simple method that painters have used for years:
- Wall area = 2 x (room length + room width) x ceiling height.
- Net area = wall area, minus doors and windows. A standard door is counted as 20 sq ft and a standard window as 15 sq ft. The ceiling area (length x width) is added if you choose to paint it.
- Paint needed = net area x number of coats x (1 + extra paint) / coverage per gallon.
Example: a 12 x 12 ft room with 8 ft walls, one door and two windows has about 334 sq ft of paintable wall. For two coats with 10% extra paint at 350 sq ft per gallon, you need about 2.1 gallons.
Paint Needed by Room Size
The table shows the paint needed for walls only, with 8 ft ceilings, one door, two windows, two coats, 10% extra paint and a coverage of 350 sq ft per gallon.
| Room size | Paintable wall area | Paint for 2 coats |
|---|---|---|
| 10 x 10 ft | 270 sq ft | 1.7 gallons |
| 10 x 12 ft | 302 sq ft | 1.9 gallons |
| 12 x 12 ft | 334 sq ft | 2.1 gallons |
| 12 x 14 ft | 366 sq ft | 2.3 gallons |
| 14 x 16 ft | 430 sq ft | 2.7 gallons |
| 16 x 20 ft | 526 sq ft | 3.3 gallons |
Paint Buying Tips
- Use primer when needed. New drywall, bare wood, stains and big colour changes often need a coat of primer first.
- Dark and bright colours. Strong colours can need three coats, especially over a light wall.
- Rough or porous walls. Brick, concrete, texture and fresh plaster soak up more paint than smooth walls.
- Ceilings. Use ceiling paint for the ceiling. It is thicker and hides marks better.
- Trim, doors and skirting. Calculate these separately, because they often use a different paint.
- Keep a little extra. Store leftover paint for touch-ups. Mix cans of the same colour together before you start.
What Changes Paint Coverage
The coverage number on the can is for ideal conditions on a smooth, primed surface. Your real coverage changes with these factors:
- Surface type: smooth, rough, porous or glossy
- Paint quality: premium paints usually cover better than cheap paints
- How you apply it: rollers, brushes and sprayers use different amounts
- Colour change: going from dark to light, or the other way, needs more coats
- Wall condition: patches and repairs soak up extra paint
Frequently Asked Questions
How much paint do I need for a 12 x 12 room?
For walls only, with 8 ft ceilings, one door, two windows and two coats, you need about 2.1 gallons including 10% extra. That means one gallon is not enough, so plan to buy two gallons or a gallon and a few quarts.
How much does one gallon of paint cover?
Most paints cover about 350 to 400 sq ft per gallon in one coat. The exact number is on the paint can, so enter that value in the calculator for the best result.
Do I need two coats of paint?
Two coats are the normal choice. They give an even colour and a lasting finish. You may get away with one coat when you repaint a similar colour with a good quality paint. Big colour changes can need three coats.
Should I include the ceiling?
Include the ceiling only if you plan to paint it with the same paint. Most people use a separate ceiling paint, so run the calculator again with the ceiling option for that paint.
Do I need to subtract doors and windows?
Yes. Deducting them stops you from buying more paint than you need. The calculator deducts 20 sq ft for each door and 15 sq ft for each window. If you have very large windows, add extra paint to be safe.
Does the calculator work in metres and litres?
Yes. Switch the units to metres and the calculator uses litres. The default coverage is 8.5 sq m per litre, and you can change it to match your paint.
Why should I buy extra paint?
Extra paint covers waste, rough patches, spills and later touch-ups. Ten percent extra is a common allowance.
Note: This calculator gives an estimate. Always check the coverage on your paint can, and ask the paint store if you are unsure about primer or the number of coats.