Square metres of a room
Floor, walls, perimeter and volume from three measurements.
Calculator inputs
Results
Enter your values and press “Calculate” to see the result.
In short
- What it calculates
- Floor, walls, perimeter and volume from three measurements.
- Formula used
Area = length × width- Example
- A 5 × 4 m room with 2.5 m ceilings:
Room area calculator
Before buying flooring, paint or air conditioning you need four different figures: the floor, the walls, the perimeter for skirting and the air volume.
Length, width and height give you all of them at once.
How it works
Floor area is length times width. Wall area is the perimeter times the height, without deducting doors and windows: for painting it is worth measuring those separately.
Formula
Area = length × width
Perimeter = 2 × (length + width)
Walls = perimeter × height
Volume = length × width × height
Worked example
A 5 × 4 m room with 2.5 m ceilings:
Floor: 20 m²
Perimeter: 18 m
Walls: 45 m²
Volume: 50 m³
Explanation
Usable and built area are not the same
Usable area is what you walk on. Built area includes the thickness of your own walls and half of party walls, and built area with common parts adds a proportional share of the entrance hall and stairs. A flat advertised at 90 square metres may have 75 usable. When comparing prices per square metre, make sure you are comparing the same measure.
Paint: deduct or not
To paint walls, multiply the perimeter by the height and deduct doors and windows. On small surfaces the difference is marginal and offsets waste; in a room with large windows, deducting them saves a whole tin.
Coats and coverage
The tin states how many square metres it covers per coat. Two are almost always needed, and over dark or new walls sometimes three. Multiplying the area by the number of coats before buying avoids running out halfway up a wall.
Volume is what matters for climate control
To size an air conditioner or calculate air changes you need volume, not area. With high ceilings, two rooms of the same floor area need different equipment.
Frequently asked questions
Should I deduct doors and windows from the walls?
For painting, yes: a door takes about 1.6 m² and a window 1 to 2 m². The paint calculator lets you enter those openings.
What is the air volume for?
For sizing heating, cooling and ventilation. Those systems are chosen by cubic metres, not square metres.
Why is my flat smaller than advertised?
The listing probably gives built area, which includes walls and sometimes common parts. Usable area, what you walk on, is always smaller.
How much paint do I need?
Multiply the area to paint by the number of coats and divide by the coverage per litre stated on the tin. Count on at least two coats.
Need to calculate something else?
These tools are often used alongside this calculator.