---
title: "Radius and Diameter"
description: "Learning video: The diameter goes straight across through the center. It is twice as long as the radius. The radius is 4 cm. How long is the diameter?"
canonical: "https://www.mathapex.app/en/math-stories/geometry/radius-and-diameter/"
language: "en"
video: "https://www.mathapex.app/media/stories/videos/en/radius-and-diameter.0948c582.mp4"
duration: "PT28S"
---

# Radius and Diameter

Learning video 61 · Geometry · Grade 4 · 0:28

## Read the story

We draw a circle with a compass.

The point stays in the center. The distance to the edge is the radius.

The diameter goes straight across through the center. It is twice as long as the radius.

**The radius is 4 cm. How long is the diameter?**

## Answer and working

Correct! 2 times 4 is 8 centimeters.

`2 × 4 = 8`