Room Dimension Calculator
Enter the floor area you want plus a proportion or one side, and the room dimension calculator gives a width and length that make up that area. Have the width and length already? The room size calculator gives the area.
Room dimension calculator
Square meters, e.g. 20 (or 215 sq ft)
Width : length, e.g. 3:4 or 1.5
- Width
- 3.87 m
- 12′ 8″
- Length
- 5.16 m
- 16′ 11″
Width × length = 20.00 m² (215.3 sq ft).
How to use it
Enter the area
In m² or sq ft. You can type the other unit too, for example 215 sq ft while in metric mode.
Choose what else you know
A proportion (type one or pick 1:1, 4:5, 3:4, 2:3 or 1:2) or the length of one side.
Read the width and length
Both are shown in meters and in feet and inches, with a check that they multiply back to your area.
Design this room
Opens the editor with a room of that width and length, measured to the wall centre lines like every room in the editor.
How the dimensions are worked out
With a proportion of width to length of a : b, the width is √(area × a ÷ b) and the length is √(area × b ÷ a). For 12 m² at 3:4 that gives 3 m by 4 m; for 200 sq ft at 1:2 it gives 10 ft by 20 ft.
With one side known, the other side is the area divided by it: 200 sq ft with a 10 ft wall needs the other wall to be 20 ft.
Same area, different rooms
Area alone says little about how a room works. 16 m² can be 4 × 4 m or 2.83 × 5.66 m: the square room takes a bed with space on three sides, while the long one is closer to a corridor with a bed at one end.
Try two or three proportions and picture the largest piece of furniture in each. If a wall length is fixed, by an existing house or a plot, switch to “One side” and let the calculator find the other.
When it helps
An extension of a set size
You know the floor area you can add; find the shapes that give it.
A room in a new house plan
Turn the area you want for each room into walls you can draw.
Fitting a gap
One side is fixed by the space available; the calculator gives the other.
Reading a listing
A listing gives only an area; see what width and length it could mean.
Frequently asked questions
How do I find the length and width of a room from its square footage?
You need one more fact: the proportion of the room or one of its sides. Divide the area by the known side, or use the proportion to split the area into a width and a length. The calculator does both.
What does a proportion of 3:4 mean?
The width is three parts for every four parts of length, so a 3:4 room is a third longer than it is wide. 1:1 is a square and 1:2 is twice as long as it is wide.
What size is a 200 sq ft room?
It depends on the shape: 10 × 20 ft at 1:2, about 12′ 3″ × 16′ 4″ at 3:4, or about 14′ 2″ square. Enter 200 and try the proportions.
What proportion should I choose?
That is up to you and the furniture you plan to use. Try a few: the result updates as you type, and the furniture layout planner shows whether your pieces fit the shape.
Can it work out an L-shaped room?
No, it gives rectangles only. For an L-shape, use the square footage calculator, which takes the overall size and the notch.
Why are the results rounded?
Widths and lengths are shown to the centimeter and to the nearest inch, so multiplying the rounded figures can differ slightly from the exact area. The room opened in the editor uses the size to the millimeter.
Ready to plan your space?
It is free, runs in your browser and needs no account. Projects are saved privately on this device.