Ruler

About this tool

Measuring is one of the first ways children connect numbers to the real world, and a ruler is where it begins. This free interactive ruler lets children measure length in centimetres and inches and see how a number describes how long something is.

Working with a ruler builds the careful habits early measurement depends on: lining up the start at zero, reading the marks in order, and naming the unit. These are the same habits children will later bring to rulers, tapes, and scales of every kind.

It runs right in the browser on tablets, phones, and classroom computers, with nothing to install and no account to create. There is no timer and no score — just a calm space to explore length and measurement.

How to use it in class

• Show the ruler on a whiteboard and point out where measuring starts — at the zero mark, not the edge.
• Measure a line together, reading the centimetres in order as you go.
• Switch between centimetres and inches to show that the same length can be named in different units.
• Compare two lengths and talk about which is longer and by how much.

Classroom ideas

• Show a measured line and ask children to read its length before you reveal the answer.
• Ask children to find something that is about a given length, then check it against the ruler.
• Measure the same object in centimetres and inches and talk about why the numbers differ.
• Order several lengths from shortest to longest and measure to check the order.