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Numbers · geometry · rectangleArea of a rectangle — formula and calculator

Work out the area of a rectangle with the formula S = a × b — your numbers substituted and a diagram drawn. The perimeter is calculated too. Units can be mixed, and the answer comes in the units you need, hectares and acres included.

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01Calculator02Formula03Example04Mistakes05Nearby06Related
01

Calculator

enter the sizes — the formula and diagram follow

Rectangle

area · perimeter
a = 5 cmb = 3 cm
diagram · not to scale
Result
Area
15cm²
= 0.0015 m²
Perimeter
16cm
= 0.16 m
How it was calculated
S = a × b = 5 × 3 = 15 cm²
P = 2(a + b) = 2 × (5 + 3) = 16 cm
← Other shapes and the composite shape
02

Formula

and what each letter means
Area
S = a × b
Perimeter
P = 2(a + b)
Notation
a
length
b
width
03

Worked example

with real numbers
Givena = 5 cm, b = 3 cm
Solution
S = a × b = 5 × 3 = 15 cm²
P = 2(a + b) = 2 × (5 + 3) = 16 cm
Answer: area — 15 cm², perimeter — 16 cm.
04

Common mistakes

Both sides must be in the same units: 5 m × 30 cm is 5 × 0.3 = 1.5 m², not 150.

The perimeter is the sum of all four sides, 2(a + b), not a + b.

05

Nearby shapes

SquareS = a²ParallelogramS = a × hRectangular boxV = a × b × cCalculatorAll 19 shapes, the composite shape and hectares →
м · км

Length converter

Metres, feet, inches, miles
кг · г

Weight converter

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%

Percent and VAT

Shares, mark-ups, VAT
2·8·16

Number bases

Binary, octal, hex

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