Area Calculator

Area is the amount of flat space inside a shape, measured in square units such as cm². This area calculator works out the area of rectangles, squares, triangles, circles, trapezoids and parallelograms. It shows the formula, substitutes your measurements, and labels the answer with the correct square unit.

How to use the area calculator

Choose the shape.
Enter its measurements and pick a unit.
Press Calculate to see the area, the formula and the steps.

Formula

A_{\text{rectangle}} = l \times w

A_{\text{triangle}} = \tfrac{1}{2} b h

A_{\text{circle}} = \pi r^2

Worked example: Rectangle 8 × 5

Shape: Rectangle
Length (l): 8
Width (w): 5
Unit: cm

✓ Answer checked

40\text{ cm}^2

Step-by-step working (2 steps)

Use the formula Area of a rectangle
The area of a rectangle:
$A = l \times w$
Substitute and calculate
Put the measurements in and work it out.
$A = 8 \times 5 = 40\text{ cm}^2$

Formulas used

A = l \times w

How this was checked

✓ Multiplying in the other order (w × l) gives the same area.

All lengths are in cm, so the area is in square cm (cm²).

Frequently asked questions

How do I find the area of a triangle?

Multiply the base by the perpendicular height and halve it. A triangle with base 10 cm and height 4 cm has an area of 20 cm².

How do I find the area of a circle?

Multiply π by the radius squared. A circle with radius 5 m has an area of 25π ≈ 78.54 m².

Why is area in square units?

Area counts how many unit squares fit inside the shape, so lengths in cm give an area in cm².

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