Room Size Calculator
Work out a room's size — from its length, width and height — in floor area, wall area, volume and perimeter.
A room is five numbers: floor area, wall area, volume, perimeter — and the doors and windows that come off the walls. This calculator is all five, from three measurements.
Enter the room; the numbers follow.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Enter the room length, width and height.
- Enter the number of doors and windows.
- Read the floor area, the net wall area, the volume and the perimeter.
Worked example
| Room | 4 m × 5 m × 2.7 m |
|---|---|
| Floor area | 4 × 5 = 20 m² (215.28 ft²) |
| Perimeter | 2 × (4 + 5) = 18 m |
| Wall area, gross | 18 × 2.7 = 48.6 m² |
| Deductions | 1 door × 1.95 + 2 windows × 1.39 = 4.73 m² |
| Wall area, net | 48.6 − 4.73 = 43.86 m² |
| Volume | 20 × 2.7 = 54 m³ |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
What is the net wall area?
The wall area minus the doors and windows — the area you actually paint or cover. A standard door deducts 1.95 m² and a window 1.39 m².
Why do I need the room volume?
For heating, ventilation and air conditioning — a room's volume decides the heater size and the air changes needed. Use it with the room heating calculator.
How do I measure a room?
Measure the length and width at floor level, and the height from floor to ceiling. For an L-shaped room, split it into two rectangles and add them.
Is this a substitute for building design?
No. This is a size calculation for planning. Structural requirements and building-code compliance vary by location — see the safety notice.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.