The Perimeter Of A Rectangle Calculator
Perimeter is the fence, the skirting and the picture frame: the distance around the edge, which is always a plain length rather than a square measure.
Perimeter
26
- Half sum (length + width)
- 13
- Area
- 40
- Diagonal
- 9.434
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
The formula this calculator uses
perimeter = 2 x (length + width)
- P
- Perimeter, the total distance around the edge
- l
- Length of the longer side
- w
- Width of the shorter side, in the same unit
How to check the result by hand
- 1
Measure one long side and one short side
You only need two measurements, not four. Opposite sides of a rectangle are equal by definition, so the other two are already known.
- 2
Convert both to the same unit
Addition is unforgiving about units. Two metres plus thirty centimetres has to become two metres plus 0.3 metres, or two hundred centimetres plus thirty centimetres, before anything else happens.
- 3
Add the length and the width
Eight plus five is thirteen. This half sum is the distance along one long side and one short side, a quarter of the way round.
- 4
Double the half sum
Two times thirteen is twenty six metres. Doubling at the end is safer than doubling each side first, because there is only one multiplication to get right.
- 5
Check against the area
The area of the same rectangle is forty square metres. A perimeter larger than the area in the same unit is not an error by itself, but a perimeter in square units certainly is.
For worked examples, common mistakes and the limits of this formula, read the full How To Calculate The Perimeter Of A Rectangle page.