How to Calculate Pythagoras' Theorem in the UK: Step-by-Step Guide

Updated · Maths

Introduction

Everyday maths comes up everywhere, from splitting a bill to checking a discount or helping with homework. A clear method makes it quick and reliable.

This guide explains how to calculate pythagoras' Theorem in the UK, step by step. Find the hypotenuse of a right-angled triangle from the two shorter sides. You'll see the formula, a fully worked example and practical tips for UK readers.

What this calculation covers

Find the hypotenuse of a right-angled triangle from the two shorter sides.

Getting the method right means you can check prices, understand statistics in the news and help children with GCSE-style questions confidently.

The method and formula

Pythagoras' theorem: a² + b² = c². The hypotenuse c is the square root of a² + b².

Every figure on our pythagoras Theorem Calculator follows this method, so you can check the working yourself.

Worked example

Here's a typical example using these figures:

InputValue
Side a3
Side b4

Running them through the method gives:

ResultValue
Hypotenuse c5
Triangle area6
Perimeter12

The headline figure is hypotenuse c: 5. Change any input and the result will move with it.

How to use the calculator

  1. Enter or choose side a.
  2. Enter or choose side b.
  3. Read your results. The main figure is shown at the top, with a breakdown underneath.
  4. Try different values to compare scenarios side by side.

Tips for UK readers

  • Write down which number is the 'whole' before working out any percentage.
  • Round only at the end of a calculation, not in the middle.
  • Check answers roughly in your head – does the result look sensible?
  • For statistics, note whether your data is a full population or a sample.

Frequently asked questions

What's the quickest way to work out pythagoras' Theorem?

Use our free pythagoras Theorem Calculator. It applies this method automatically: Pythagoras' theorem: a² + b² = c². The hypotenuse c is the square root of a² + b².

Are these suitable for GCSE revision?

Yes. The methods match those taught in UK schools, and each page explains the formula used.

How many decimal places are shown?

Most results show up to two decimal places. Use the rounding in your working as your teacher or exam board requires.

Can I use negative numbers?

Yes, where they make sense mathematically, such as percentage change.

Summary

To work out pythagoras' Theorem, follow the method above: Pythagoras' theorem: a² + b² = c². For a quick, accurate answer with your own figures, use the calculator.

Try the pythagoras Theorem Calculator

Enter your own figures and get an instant answer – free, no sign-up.

Open the pythagoras Theorem Calculator

Next, read Pythagoras' Theorem: Common Mistakes, Tips and FAQs.

More maths guides

This guide is general information, not financial, tax, legal or medical advice. Figures use 2025/26 UK rates where relevant. Always check GOV.UK or NHS.uk for official guidance.