How to measure a room
Measure wall to wall at floor level, in feet, and write each number down as you go. For flooring, measure the open floor including closets that will get the same flooring; for paint, you need wall area instead (see the paint calculator). Round each measurement up to the next inch rather than down. A 1 in error on both sides of a 12 × 10 ft room adds or removes nearly 2 sq ft.
If walls aren’t square, measure the length at both ends and use the larger figure. For a bay window or rounded alcove, measure across the opening (the diameter) and treat the bump-out as a half circle.
Breaking an odd room into shapes
Almost any floor plan can be split into rectangles, triangles and circles:
- L-shaped room: two rectangles that do not overlap. Or measure the full outer rectangle and subtract the missing corner — whichever needs fewer measurements.
- Angled wall: a rectangle plus a triangle. The triangle’s height must be measured square to its base, not along the sloped wall.
- Island, built-in or tub: add the whole room, then add a section set to Subtract for anything the flooring won’t cover.
- Round room or bay: a circle or half circle using the diameter.
The calculator takes up to five sections. Unused sections are simply ignored.
Worked example
The default setting is a single 12 × 10 ft room. Here it is with an L-shaped extension, a closet carve-out and 10% waste:
| Section | Shape | Calculation | Area |
|---|---|---|---|
| 1 (add) | Rectangle 12 × 10 ft | 12 × 10 | 120 sq ft |
| 2 (add) | Rectangle 6 × 8 ft | 6 × 8 | 48 sq ft |
| 3 (subtract) | Rectangle 3 × 2 ft | 3 × 2 | −6 sq ft |
| Total | 120 + 48 − 6 | 162 sq ft | |
| In square yards | 162 ÷ 9 | 18 sq yd | |
| With 10% waste | 162 × 1.10 | 178.2 sq ft |
At a material price of $4.00 per sq ft, 178.2 sq ft costs $712.80. On its own, the default 12 × 10 ft room is 120 sq ft, or 13.33 sq yd.
Choosing a waste allowance
Waste defaults to 0% so the tool gives a plain measurement. Add waste when you are buying material:
- Plank or sheet flooring laid straight: roughly 5–10%, more for rooms with many corners.
- Diagonal or herringbone patterns: typically 15% or more, because every edge piece is an angled cut.
- Carpet: depends on roll width and seam placement more than area, so ask the installer to measure.
Material-specific tools handle this in more detail: use the flooring calculator for boxes of plank or laminate and the tile calculator for tile, grout and thinset.
Square feet, square yards and square meters
One square yard is 3 ft × 3 ft, or 9 sq ft. Carpet and some sheet vinyl are still priced per square yard, so the calculator shows both. Switch to metric to see square meters (1 m² ≈ 10.76 sq ft). Make sure prices and quantities use the same unit — a carpet quote of $30 per sq yd is about $3.33 per sq ft.
Common mistakes
- Mixing inches and feet. Enter 10 ft 6 in as 10.5 ft, not 10.6.
- Overlapping sections. If two added rectangles overlap, the overlap is counted twice. Split along a wall line so pieces meet edge to edge.
- Subtracting too much. If subtracted sections add up to more than the added area, the calculator shows 0 and warns you. Check the add/subtract setting on each section.
- Using slope length on a triangle. The height must be perpendicular to the base.
For walls and ceilings rather than floors, the drywall calculator works from room dimensions and openings.
How this calculator works
- Rectangle = length × width. Triangle = ½ × base × height. Circle = π × (diameter ÷ 2)². Half circle = ½ × π × (diameter ÷ 2)².
- Total area = sum of added sections − sum of subtracted sections, floored at zero.
- Square yards = square feet ÷ 9. Area with waste = total area × (1 + waste%).
Assumptions and limitations
- Each section is a flat, simple shape measured in feet; sloped or curved surfaces are treated as flat.
- Triangle height is measured square (perpendicular) to the base, not along a slanted side.
- Subtracted sections lie entirely inside the added area; overlaps between added sections are not detected.
- Waste is applied to the net area after subtractions.
- The cost is area with waste × your price per sq ft — material only, no labor or underlayment.
These results are planning estimates, not quotes. Local prices, site conditions and building codes vary, so get written estimates from licensed contractors before you commit to a budget.
Try your own numbers. Every price and assumption above is editable in the estimator.
Back to the square footage estimatorFrequently asked questions
How do I measure an L-shaped room?
How many square feet are in a square yard?
Should I subtract a kitchen island or closet?
Sources and data
This calculator uses standard geometry and doesn't rely on external price data.
Prices are US national ranges reviewed October 2026 (data version 2026.10). A few values are editorial estimates where no single published source exists; the Cost Index marks each one. Read our methodology and editorial policy.