Rectangle Area & Perimeter Calculator
Rectangle calculator: area, perimeter and diagonal from length and width, or a side from the area.
A = l · w
How to use this calculator
- Choose the quantity you want under “Solve for”.
- Type the known values and pick their units: any combination works.
- The result updates as you type. Open “Show the steps” to see the substitution.
Area A = l × w, perimeter P = 2(l + w) and diagonal d = √(l² + w²).
Handy for rooms, plots, flooring and paint estimates.
Formula
A = l · w
| Symbol | Quantity | Units |
|---|---|---|
| l | Length | m, km, cm, mm, µm, nm, pm, Å, in, ft, yd, mi, nmi, au, ly |
| w | Width | m, km, cm, mm, µm, nm, pm, Å, in, ft, yd, mi, nmi, au, ly |
| A | Area | m², km², cm², mm², ha, ft², in², yd², ac, mi² |
Worked example
Given: l = 5 m · w = 4 m
A = l · w
Result: A = 20 m²
Frequently asked questions
What is the area of a 5 m × 4 m room?
20 m², with a perimeter of 18 m.