Floor Area Calculator
Get the floor area, perimeter and waste-adjusted area for a room. These three numbers feed almost every other flooring and renovation calculator.
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Formula and method
Area is length multiplied by width. Perimeter is twice the sum of length and width. The waste-adjusted area adds the waste percentage to the raw area.
Area, waste and the perimeter are three outputs
Length times width is the floor, the waste percentage is what you actually buy, and the perimeter is the skirting. They are related but not interchangeable: a 20 m² room buys 21 m² of laminate and needs 18 m of skirting before doors are deducted.
The waste percentage belongs to the material, not to the room. Laminate takes 5 %, tiles in a straight lay 10 %, tiles on the diagonal 15 %, and carpet often 10 % because of the roll width rather than the cuts.
Why geometry beats area for waste
A 20 m² room that is 2 × 10 m wastes more than a 4 × 5 m room of the same area, because every row ends in a long cut. Before trusting a waste figure, look at the room's shape: the more elongated or the more corners, the closer to the top of the range.
Bays, alcoves and door recesses are measured as their own rectangles and added. A recess 0.9 m deep and 0.9 m wide is 0.81 m² — small on its own, but there are usually three or four of them in a flat.
One room at a time, then add
Calculate each room separately and round up per room. Rounding once at the end across five rooms systematically under-buys, because each room's leftover is too small to help the next one.
Check the sum against the total floor of the flat before ordering. A 55 m² flat does not have 55 m² of flooring: the walls, the services riser and the bathroom tile take a share, and the measured rooms usually add up to 90 to 95 % of the stated area.
How to measure the inputs
- Run the tape along the floor from wall to wall, not along the skirting.
- Measure both ends of the wall and use the larger value.
- Check ceiling height separately if you also need wall or volume figures.
Worked example
Room length 13.12 ft; Room width 16.4 ft; Waste 10 % → Floor area with waste: 236.81 ft²
Reference data
| Room, m | Area, m² | Perimeter, m |
|---|---|---|
| 3 × 4 | 12 | 14 |
| 4 × 5 | 20 | 18 |
| 5 × 6 | 30 | 22 |
| 6 × 8 | 48 | 28 |
The perimeter is what you need for skirting and wall area, not just the area.
Practical tips
- Measure at the widest point of each wall: rooms are rarely perfectly rectangular.
- Note measurements on a sketch so you can reuse them in the other calculators.
- For open-plan spaces, treat each functional zone as its own rectangle.
Sources
- СП 54.13330.2022 — Здания жилые многоквартирные
Checked and updated October 22, 2026