📏 Measurement (cm and in)

Introduction

Measurement is how we find out the size or length of something. Two common units are:

• Centimeters (cm): used in the metric system. 1 meter = 100 cm.
• Inches (in): used in the US customary system. 1 foot = 12 inches.

The key relationship is: 1 inch ≈ 2.54 cm. That means every inch is about 2 and a half centimeters.

Examples

Let’s look at some real-world measurements:

• A crayon might be 10 cm long, which is about 4 in.
• A sheet of paper is about 28 cm tall, or 11 in.
• A smartphone is around 15 cm, or 6 in.

Conversion Practice

Convert between centimeters and inches:

Centimeters ➡ Inches:
Convert

Inches ➡ Centimeters:
Convert

Interactive Measurement Tool

Use the canvas below to measure objects. Click the buttons to switch between a centimeter ruler and an inch ruler.

Practice Problems

1. Your pencil is 12 cm long. About how many inches is it?
2. A notebook is 8 inches wide. How many centimeters is that?
3. If a toy car is 20 cm long, is that longer or shorter than 10 inches?

Think: Use the fact that 1 in = 2.54 cm to solve these!

Summary

- Measurement tells us how long something is.
- We use cm in the metric system and in in the US system.
- 1 in ≈ 2.54 cm.
- You can convert back and forth using this relationship.
- Practice helps you get familiar with both units!