Short answer: paint and wallpaper use the walls; flooring uses the floor; none of the three calculators includes the ceiling. Measure in feet and inches, turn inches into decimals, and type each number into the calculator that needs it.
1. Turn feet and inches into decimals
| Inches | Decimal feet | Example |
|---|---|---|
| 3 in | 0.25 ft | 10 ft 3 in = 10.25 ft |
| 6 in | 0.5 ft | 10 ft 6 in = 10.5 ft |
| 9 in | 0.75 ft | 10 ft 9 in = 10.75 ft |
| any inches | inches ÷ 12 | 10 ft 4 in = 10 + 4 ÷ 12 = 10.33 ft |
The paint and flooring calculators take feet; the wallpaper calculator takes inches (multiply feet by 12: 8 ft = 96 in).
2. Walls, for paint
Measure the room length, the room width and the wall height. Room mode adds all four walls: 2 × (length + width) × height. A 12 ft × 10 ft room with 8 ft walls: 2 × (12 + 10) × 8 = 352 sq ft. For a single wall, use “One wall” mode with that wall’s width and height. If you already have a wall area from a plan, use “Total area”.
3. Openings you want to subtract
Measure each door and window: width × height. Example: a door 3 ft wide and 6 ft 8 in high is 3 × 6.667 = 20 sq ft; a 3 ft × 4 ft window is 12 sq ft; together 32 sq ft. Type the total into “Area of doors & windows”. If you skip this, the calculator simply buys a little more paint. Wallpaper does not subtract openings at all (strips must match across them).
4. One wall, for wallpaper
Measure the wall’s width and height in inches. 10 ft wide = 120 in; 8 ft high = 96 in. Then copy the roll width, roll length, pattern match and repeat from the label. Measure each wall separately if the heights differ.
5. The floor, for flooring
Measure the room’s width and length at floor level: 12 ft × 10 ft = 120 sq ft. For an L-shaped room, split it into two rectangles that do not overlap and calculate each, or add the areas if the same product goes everywhere.
What is not measured here
Ceilings and trim (paint them with a separate calculation using their own product), sloped or curved walls, and stairs. The calculators are for quantity planning, not installation.
Now use the numbers
Paint calculator · Wallpaper calculator · Flooring calculator
Numbers in the tables were calculated by hand and checked against the site’s calculation code and its automated tests on 2026-09-08. They describe the examples shown, not any specific product.