Paint & Wallpaper Coverage Calculator
Estimate wall paint in gallons or liters, or wallpaper rolls with repeat and trimming allowances.
Results are provided as is, for general information. Check anything important before relying on it. See the Terms of Use.
About this tool
Estimate paint for four rectangular room walls in gallons or liters, or use Wallpaper rolls to count full-height strips and whole rolls. Paint mode subtracts door/window area, multiplies by coats and divides by editable product coverage. US feet and gallons are the initial view; changing units converts dimensions and product coverage. Wallpaper mode uses roll width and length, trimming per strip and a free or straight pattern repeat; it rounds strip counts separately for each wall. Openings are not deducted and narrow leftovers are not reused around corners. Wallpaper estimates exclude spare rolls, ceilings, slopes, murals and offset/drop-match patterns. Check your product dimensions and installation instructions.
How it works
Wall area = 2 × (length + width) × height Paintable = Wall area − doors and windows Paint units = Paintable × coats ÷ coverage per unit (round up)
Four walls of a room add up to the perimeter times the height. Subtract the area of doors and windows, multiply by the number of coats, and divide by how much one can covers. Always round up: you cannot buy part of a can.
| Question | Working | Answer |
|---|---|---|
| A 5 m × 4 m room with 2.5 m walls, 6 m² of openings, 2 coats, 10 m² per litre. How much paint? | 2 × (5 + 4) × 2.5 = 45; 45 − 6 = 39; 39 × 2 ÷ 10 | 7.8 litres, so buy 8 |
| A 12 ft × 10 ft room, 8 ft walls, 20 sqft openings, 2 coats and 350 sqft per gallon? | 2 × (12 + 10) × 8 = 352; (352 − 20) × 2 ÷ 350 | 1.8971 gallons, so buy 2 |
| Wallpaper a 4 m × 3 m room with 2.4 m walls, 0.5 m × 10 m rolls and 0.1 m trimming, no repeat? | 2 × ceil(4 ÷ 0.5) + 2 × ceil(3 ÷ 0.5) = 28 strips; cut length 2.5 m; floor(10 ÷ 2.5) = 4 strips per roll | 7 rolls |
| Same wallpaper room with a straight 0.6 m pattern repeat? | ceil(2.5 ÷ 0.6) × 0.6 = 3 m per strip; floor(10 ÷ 3) = 3 strips per roll; ceil(28 ÷ 3) | 10 rolls |
When to use it
Questions
How many wallpaper rolls do I need?
Switch to Wallpaper rolls and enter the room and actual roll dimensions in the same unit. Each wall needs its width divided by roll width, rounded up to whole strips. Add trimming to wall height, round the cut length up to a whole pattern repeat when required, and count only complete strips per roll. Divide total strips by strips per roll and round up. This model supports free and straight matches; it does not model offset matches. Openings are not deducted; buy any extra spare rolls separately.
Which paint coverage should I enter?
Use the coverage printed on your paint label in the selected units. The initial 350 sqft per US gallon is an editable example, not a promise of your product's yield. Switching to metric converts that same rate to about 8.5898 m² per liter; it does not select another product. Overwrite the example with the actual coverage before estimating your purchase.
Does it include the ceiling?
Walls only. Calculate ceiling paint separately as length × width × ceiling coats ÷ ceiling-paint coverage. Add that unrounded amount to the unrounded wall quantity before rounding up. Do not enter a ceiling as a room with an invented wall height.
Why one combined 'doors & windows' number instead of separate fields per opening?
Keeps the input simple for rooms with several openings. Add up the openings yourself — a standard interior door is roughly 1.6-1.9 m² (17-20 sqft), an average window 1-1.5 m² (10-15 sqft) — and enter the total.
Why does 'buy at least' round up to a whole unit?
Paint is sold in fixed can sizes, not by the exact liter or gallon, so a result like '6.6 liters needed' means you actually need to buy 7 liters' worth of cans. Rounding down would leave you short before the job is done.
Does the second coat really need just as much paint as the first?
This tool assumes coverage scales linearly with coat count, which is the simple, safe assumption to buy against. In practice a second coat can go slightly further once the first coat has sealed a porous surface — a real-world margin in your favor, not one the estimate relies on.