Area of a Rectangle Formula
Geometry Formulas: Area, Volume, Perimeter
What is the formula for the area of a rectangle?
Answer
Area of a rectangle
A = a · b
Here a is the side (or base), b is the second side. The result comes out in square units.
Where the formula comes from
A = a · b
Rule the rectangle into unit squares: b rows of a squares each. Counting them is multiplication, and that is the whole derivation — every other area formula on this site is eventually reduced to this one.
Worked examples
Let a = 8, b = 5. Then the area of a rectangle = 40 square units.
Let a = 12.5, b = 4. Then the area of a rectangle = 50 square units.
The common mistake
Mixing units — multiplying metres by centimetres. The product is not meaningless, it is in m·cm, which is nobody's idea of an area: convert both sides to the same unit first and the answer lands in m² or cm².
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 = | Area |
|---|---|
| 1 | 5 square units |
| 2 | 10 square units |
| 3 | 15 square units |
| 4 | 20 square units |
| 5 | 25 square units |
| 10 | 50 square 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 area of a rectangle? (The answer is: A = a · b). Pick the pair — "Area of a circle", for instance — and hit the "Find out" button.
Geometry Formulas: Area, Volume, Perimeter