How to Calculate the Square Metres of a Room

The basic rectangle

Most rooms are rectangles, so their area is simply length times width. Measure both sides in the same unit — metres are easiest — and convert any centimetres early: 350 cm is 3.5 m. A room 5 m by 4 m is 20 m². Getting the units right before you multiply avoids the single most common mistake in these calculations.

Irregular and L-shaped rooms

An awkward shape becomes easy once you split it into rectangles. Draw the room, divide it along a straight line into two or more rectangles, find each area with length × width, and add them. If there is a permanent cut-out like a chimney breast, calculate it as its own rectangle and subtract it from the total.

Circles and triangles

Not every space is rectangular. For a circular area, the formula is π × radius², where the radius is half the diameter — a round patio 4 m across has a 2 m radius, so π × 2² ≈ 12.6 m². For a triangle, it is half the base times the height. Combine these with rectangles to measure almost any floor plan.

Why area matters

Almost every material you buy for a room is sized off its area: paint by the square metre it covers, flooring and tiles by the pack, carpet by the roll, even heating by the space to warm. An error here multiplies into wasted money or a second trip to the shop, so measure twice, keep your units consistent, and add a small margin for cuts and waste.

Frequently asked questions

How do I convert square feet to square metres?

Multiply the square feet by 0.0929. So 200 sq ft is about 18.6 m².

How do I measure an L-shaped room?

Split it into two rectangles along a straight line, calculate each one's area, and add them together.

What's the formula for the area of a circle?

Area = π × radius², where the radius is half the diameter — so a 4 m circle is π × 2² ≈ 12.6 m².