Area Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/3/2026
The area of a rectangular room is found by multiplying its length by its width. Example: a room measuring 4 m by 3 m has an area of 12 m².
Explanation
This basic calculation is the starting point for many DIY projects: how much paint you need, flooring, tiling, or carpet. For a room that isn't perfectly rectangular (an L-shape, an alcove), break it down into several rectangles, calculate the area of each separately, then add the results together. The perimeter shown here (the sum of the four sides) is useful, for example, for estimating the length of baseboards or molding needed to line the room.
Example: a 4 m x 3 m room
Inputs
Length: 4 m. Width: 3 m.
Calculation
Area = length × width = 4 × 3 = 12 m². Perimeter = 2 × (4 + 3) = 14 m.
Result
The room has an area of 12 m², with a perimeter of 14 m.
Frequently asked questions
How do I calculate the area of an L-shaped room?
Break the room down into two (or more) simple rectangles, calculate the area of each separately with this calculator, then add the results together.
Should I subtract the area of doors and windows?
It depends on the use: for flooring, no (the floor stays covered). For a quantity of wall paint, technically yes, but many DIYers keep a small safety margin rather than precisely subtracting small openings.
What unit should I use for length and width?
This calculator expects meters. If you have measurements in centimeters, divide them by 100 before entering them (for example, 350 cm becomes 3.5 m).