Room Area Calculator

Floor area is the first number in almost every home project: flooring packs, paint, AC sizing and property listings all start here. This calculator handles rectangular rooms plus an optional alcove or niche.

It also gives you the perimeter — the number you need for skirting boards (baseboards) and coving.

Enter valid values to see the results.

Formula

Area = length × width (+ alcove length × alcove width); Perimeter = 2 × (length + width)

Measure in metres for m² or feet for ft². To convert: 1 m² = 10.764 ft². For L-shaped rooms, treat each rectangle as “room + alcove” or calculate separately and add.

How to measure

Measure at floor level, wall to wall, at the longest points — skirting boards can hide 1–2 cm of error at eye level.
For alcoves, bay windows and niches, measure their length and width separately and enter them in the optional fields.
Measure twice: a 10 cm error on a 5 m wall changes the area of a 20 m² room by 2%.

Worked example

A 5 × 4 m room with a 1.5 × 0.8 m alcove: main area 20 m², alcove 1.2 m², total 21.2 m² (228 ft²). Perimeter 18 m — buy 18 m of skirting plus 10% for cuts.

Practical tips

Sketch the room first and label every wall — it prevents double-counting alcoves.
For flooring, always order by area plus waste, not by room name (“bedroom packs” do not exist).
Property listings often quote gross area including walls; your measured net area will be 3–5% smaller.
Keep a note of each room’s area — you will reuse it for paint, flooring and heating calculations.

Waste allowance

Area itself needs no waste allowance — waste applies to the materials you buy for it (see the Flooring and Tile calculators).

Quick area conversions

Square metres	Square feet	Typical room
10 m²	108 ft²	Small bedroom
15 m²	161 ft²	Bedroom / office
20 m²	215 ft²	Living room
30 m²	323 ft²	Large living room
40 m²	430 ft²	Open-plan kitchen-living

Common mistakes

1 Measuring at chest height where walls may bow — always measure at floor level.
2 Forgetting alcoves and bay windows, then running out of flooring at the end of the job.
3 Mixing metres and centimetres (entering 450 instead of 4.5 m).
4 Using gross listing area for material orders — measure the actual room.

Frequently asked questions

How do I calculate the area of a room?

Multiply length by width. A 5 × 4 m room is 20 m². For L-shaped rooms, split into rectangles, calculate each and add them.

How do I convert m² to ft²?

Multiply square metres by 10.764. A 20 m² room is about 215 ft². To go the other way, divide ft² by 10.764.

How do I measure an irregular room?

Split the floor plan into rectangles (and triangles if needed: base × height ÷ 2), calculate each area, and add them together.

What is the perimeter used for?

Skirting boards (baseboards), coving, and wallpaper borders are all bought by perimeter length. Deduct door widths (about 0.9 m each) for skirting.

Does floor area include closets?

For material ordering, yes — flooring goes into closets. For property measurement standards, rules vary by country.