# Circle Area & Circumference Example

Calculate circle area and circumference in Calcul.io with pi and a measured radius, keeping the geometry formula visible and editable.

## Circle measurements

Enter a measured radius and keep both common circle formulas visible. The sample uses a radius of 3.5 metres.

```calculio
radius = 3.5 m
area = pi * radius ^ 2
circumference = 2 * pi * radius
```

## How it works

1. Replace `radius` with the measurement from your drawing or object.
2. Review `area` for the surface inside the circle.
3. Use `circumference` for the distance around its edge.

Try changing the unit to centimetres or inches and let the result keep the corresponding square unit for area.

[Next: solve a quadratic in simple steps](https://calcul.io/examples/quadratic-equation/index.md)