Perimeter of a Rectangle Formula
Geometry Formulas: Area, Volume, Perimeter
What is the formula for the perimeter of a rectangle?
Answer
Perimeter of a rectangle
P = 2 · (a + b)
Here a is the side (or base), b is the second side. The result comes out in units.
Where the formula comes from
P = 2 · (a + b)
Walk the outline: a, then b, then a again, then b again. Two of each, so 2a + 2b, which is 2(a + b).
Worked examples
Let a = 8, b = 5. Then the perimeter of a rectangle = 26 units.
Let a = 12.5, b = 4. Then the perimeter of a rectangle = 33 units.
The common mistake
Answering with the area. Perimeter is a length and comes out in metres; area is a length squared and comes out in square metres. The two formulas take the same two numbers, which is exactly why they get swapped.
Other quantities: Rectangle
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See Also
- Square Footage Calculator - Width × length in feet to square feet
- Square Feet to Square Meters (Sq Ft to Sq M) - Convert Square Feet to Square Meters
- Square Meters to Square Feet (Sq M to Sq Ft) - Convert Square Meters to Square Feet
- Gravel Calculator - Area to cubic yards, tons and coverage
- Topsoil Calculator - Cubic yards, weight and coverage for any area
- Multiplication Facts - Any two numbers from 1 to 9, with the working shown
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Values from the Formula (b = 5)
| If a = | Perimeter |
|---|---|
| 1 | 12 units |
| 2 | 14 units |
| 3 | 16 units |
| 4 | 18 units |
| 5 | 20 units |
| 10 | 30 units |
Geometry Formulas: Area, Volume, Perimeter
These are the formulas for the area, perimeter, circumference, volume and surface area of the standard shapes — 31 of them. Each page shows not only the formula but where it comes from, what every letter stands for, two worked examples and the mistake that this particular shape invites. For example, it can help you find out what is the formula for the perimeter of a rectangle? (The answer is: P = 2 · (a + b)). Pick the pair — "Area of a circle", for instance — and hit the "Find out" button.
Geometry Formulas: Area, Volume, Perimeter