---
title: "Comparing lengths by measuring"
description: "Measure to find how much longer one object is than another. Give the length difference in a standard unit of length."
canonical: https://lightmysky.com/learn/mathematics/comparing-lengths-by-measuring-mt_xWg0lI_gG4
source: https://lightmysky.com/learn/mathematics/comparing-lengths-by-measuring-mt_xWg0lI_gG4.md
retrieved: 2026-11-12
---

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# Comparing lengths by measuring

Measure to find how much longer one object is than another. Give the length difference in a standard unit of length.

Subject: Mathematics · Area: Measurement · Ages 7 to 8
Page: https://lightmysky.com/learn/mathematics/comparing-lengths-by-measuring-mt_xWg0lI_gG4

## Ready when they can

- Measure two objects and calculate the difference in length
- Express the difference using the correct unit (e.g. '7 cm longer')
- Solve a comparison problem: 'How much taller is the bookshelf than the desk?'

## Lesson: Comparing lengths by measuring

Measure both objects in the same unit. Compare length with length, width with width, or height with height. Subtract the smaller measurement from the larger one to find the difference. Say the unit and which object is longer, wider or taller. If one is longer by an amount, the other is shorter by that same amount.

*(drawing: Both measurements are heights. 15 - 6 = 9, so the flower is 9 cm taller than the seedling.)*

**Example.** Mia's book is 22 cm long and her notebook is 15 cm long. Count up from the shorter length: 15 to 20 adds 5, then 20 to 22 adds 2. The gap is 5 + 2 = 7 cm. Her book is 7 cm longer.

For larger gaps, count up in easy parts. From 30 cm to 54 cm, add 10 to reach 40, then add 14 to reach 54. The difference is 10 + 14 = 24 cm. Check by addition: 30 + 24 = 54. The shorter length plus the difference should equal the longer length.

A comparison can help you find a missing height. A box is 14 cm tall. A plant is 6 cm taller, so its height is 14 + 6 = 20 cm. A shelf is 53 cm tall. A stool is 21 cm shorter. Subtract 20 to reach 33, then 1 to reach 32 cm.

Equal measurements have a difference of zero. Neither object is longer. If measurements use different units, measure both again in one unit before subtracting. A quick look may show which object is taller, but it does not give the exact measured difference.

**Recap.** Measure both objects in the same unit, then subtract to find how much longer one is.

*Lesson, questions and flashcards written for this dataset.*

## Practice

14 questions on this page, each with its working shown.

## Needs first

- [Measuring length (age 7+)](https://lightmysky.com/learn/mathematics/measuring-length-age-7-mt_e4x3l2JeLI)
- [Ordering and Comparing Lengths](https://lightmysky.com/learn/mathematics/ordering-and-comparing-lengths-mt_skYly2Qm01)

## Opens up

- [Length word problems within 100](https://lightmysky.com/learn/mathematics/length-word-problems-within-100-mt_DLcEzmmj2r)