How to measure a room for paint, flooring and tile
· 7 min read
Paint is bought by wall area, flooring and tile by floor area, and all three come from the same three numbers: length, width and ceiling height. Measure a room once, properly, and you can order everything for it. This walks through the measuring, the deductions, the waste allowances that change with the pattern, and the round-up to whole boxes, with a 12 x 12 ft room worked out at the end: 2 gallons of wall paint, 8 boxes of flooring, or 16 boxes of tile.
3D room plannerPaint calculatorTile calculator
Start with one accurate measurement
Tape or laser: measure the length and width of the room at floor level, wall to wall, in two places each (rooms are rarely square; use the larger figure). Measure the ceiling height in a corner. Then measure each door and window, width and height. Write it all down before you open a single calculator: length, width, height, openings. For an L-shaped or irregular room, split it into rectangles and measure each one; the room planner lets you draw the outline and gives floor, ceiling, wall and skirting figures for the whole shape.
Walls for paint: perimeter, height, minus openings
Wall area is the perimeter times the ceiling height. For the 12 x 12 room with an 8 ft ceiling that is 2 x (12 + 12) x 8 = 384 square feet. Take off the openings: one door and two windows are about 46 square feet here, leaving 338. Divide by the coverage on the can, 350 square feet per gallon in this example, multiply by two coats and round up: 1.93 gallons, so 2. The ceiling is its own surface, 144 square feet with nothing to subtract, 0.82 gallons for two coats. The paint calculator does the sum for any coverage and can size, and the 12x12 room guide has 9 and 10 ft ceilings too.
Floors for flooring and tile: length times width, plus waste
Floor area is simply length times width: 144 square feet. Closets get floored, so add them; doorways are floored to the threshold; fitted units that stay put are not. Then add waste, which is where most people under-order. Waste is not carelessness, it is geometry: every row ends in a cut, and the offcut is only reusable if it is long enough to start the next row.
| Layout | Extra to buy |
|---|---|
| Straight grid, simple rectangular room | 10% |
| Offset or brick pattern (planks, 12x24 tiles) | 10 to 12% |
| Diagonal layout | 15% |
| Herringbone, chevron, borders | 15 to 20% |
| Room with alcoves, islands, many corners | add 5% to the above |
| Natural stone, large format (chips on cutting) | add 5% to the above |
From square feet to boxes
Flooring is sold by the box, labelled in square feet: divide the area with waste by the box coverage and round up. 158 square feet in boxes of 20 is 7.92, so 8 boxes. Tile is sold by the box too, but counted in pieces: a 12 x 12 inch tile with its 1/8 inch grout line covers a little more than a square foot, so 144 square feet is 142 tiles before waste and 156 after 10%, which is 16 boxes of 10. The tile calculator takes any tile size, grout width and box count, and the 12x12 tile guide has the common sizes and areas already worked out. The round-up matters: a fraction of a box is a whole box you have to buy, and an extra box from the same batch is cheap insurance against the one you cannot match later.
Irregular rooms, alcoves and mixed flooring
Break the room into rectangles that add up to the whole floor and measure each; an alcove is one more rectangle, a bay window another. Where two floorings meet in a doorway, decide where the threshold goes and measure each side to it. Stairs are risers plus treads, each measured; a landing is a small room. For the walls of an irregular room the perimeter still works: add up every wall length, including the short returns into alcoves, and multiply by the height.
Shopping list for a 12 x 12 room
One measurement, 12 x 12 ft with an 8 ft ceiling, 1 door and 2 windows, through the three calculators:
| Item | Quantity | Order |
|---|---|---|
| Wall paint, two coats | 1.9 gal | 2 gallons |
| Ceiling paint, two coats | 0.8 gal | 1 gallon |
| Plank flooring, 10% waste | 158 sq ft | 8 boxes of 20 sq ft |
| 12 x 12 in tile, straight, 10% waste | 156 tiles | 16 boxes of 10 |
| 12 x 12 in tile, diagonal, 15% waste | 163 tiles | 17 boxes of 10 |
Flooring and tile are alternatives, of course; the list shows both so you can see how the same 144 square feet turns into boxes of each. Skirting is the perimeter minus the door widths, 45 ft here, and the room planner reports it alongside the surfaces.
Quoting the whole room for a client?
The calculators give the material list for paint, flooring and tile from one measurement. The Pro quote builder adds labour, extras, margin and tax on top and prints it with your logo, so the quote goes out the same day you measured.
Frequently asked questions
- How much extra flooring should I buy for waste?
- 10% for a straight layout in a plain room, 15% for diagonal, and 15 to 20% for herringbone or chevron. That covers the cuts at the walls, the offcuts too short to reuse and a few damaged boards. For a 12 x 12 room that is 158 square feet instead of 144.
- How do I measure a room for paint if it has several windows and doors?
- Measure the perimeter and multiply by the ceiling height for the gross wall area, then measure each opening and take it off. A standard door is about 20 square feet and a window 12 to 15; large windows and patio doors are worth measuring. In the 12 x 12 example one door and two windows take 46 square feet off 384.
- How many boxes of tile do I need for a 12x12 room?
- 156 tiles of 12 x 12 inches with a 1/8 inch grout line and 10% waste, which is 16 boxes of 10 or 11 boxes of 15. Check the count or the square feet printed on the box, divide, and round up.
- Do you subtract closets and doorways when measuring for flooring?
- Add closets: they get the same floor. Doorways are usually floored too, up to the threshold, so include them. What you do not include is the area under built-in units and fitted furniture that will not be moved, such as a kitchen island or a bath.
- What waste percentage should I use for diagonal or patterned tile?
- 15% for diagonal, up to 20% for herringbone and borders. Diagonal cuts every tile along two walls and the offcuts rarely fit anywhere else. For the 12 x 12 room that is 163 tiles instead of 156.
- How many square feet does one gallon of paint cover?
- About 350 to 400 square feet with one coat on smooth, previously painted walls, the figure printed on most cans. The example uses 350. Textured or bare surfaces cover less, and two coats halve the number; the gallon coverage guide has the table by surface type.
Figures are planning estimates from the calculators on this site and typical product data. Check the yield, size or coverage printed on what you buy, round up, and follow your local building code for structural work.