Room Area Calculator

Get the four basic numbers for a room — floor area, ceiling area, perimeter and volume — from one set of measurements.

Formula and method

Floor and ceiling area are length times width, the perimeter is twice the sum of length and width, and the volume is floor area multiplied by height.

How to measure the inputs

Measure floor length and width at the widest points.
Measure floor to ceiling in at least two corners.
Sketch the room and note any protrusions or recesses.

Worked example

Room length 19.69 ft; Room width 13.12 ft; Room height 9.19 ft → Floor area: 258.33 ft²

Practical tips

Record the measurements once and reuse them in the paint, wallpaper and flooring calculators.
Measure the height in each corner: ceilings are not always level.
Include cupboards only if they are being decorated too.

Assumptions

The room is rectangular with a flat ceiling at a single height.
The floor and ceiling areas are equal, which is typical for a plumb room.
Sloped ceilings, bay windows and open stairwells need separate treatment.

Frequently asked questions

What can I do with the volume?

Volume is used for heating and ventilation calculations, and for estimating dehumidifier or air-conditioning capacity.

Why is the ceiling area shown separately?

Ceilings are often painted or plastered as a separate item, and ceiling paint is usually priced and specified independently of walls.

What if my room is L-shaped?

Split it into rectangles, calculate each one and add the areas. Perimeters should be measured along the real wall lines rather than summed from the parts.

Related calculators

Estimate only

Results are material quantity estimates only. They are not structural design, and they are not a substitute for local building codes, engineer approval or manufacturer instructions.

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