GlossariesA Level GlossariesA Level Maths GlossaryLogarithm

Logarithm - A Level Maths Definition

Reviewed by: Mark Curtis

Last updated

5 March 2025

What is a logarithm?

In A Level Maths, a logarithm is a mathematical function that tells you what power you need to raise a given base number to in order to get a specific value.

Logarithms (logs) are written as $\log_{a} (b) = c$ , pronounced 'log base $a$ of $b$ ', where $a$ is the base number, $b$ is the specific value you want and $c$ is the power. For example, $\log_{2} (8)$ represents the power of 2 that gives you 8. This is 3 (because $2^{3} = 8$ ) so

$\log_{2} (8) = 3$

If a log is written without a base in A Level, i.e. as $\log (. . .)$ , it means log of base 10, $\log_{10} (. . .)$ . If a log is written as $\ln (. . .)$ , it means log of base $e$ (called a natural logarithm).

Logarithm revision resources to ace your exams

You can find out more about logarithms by reading our revision notes. We also have exam questions on logarithms to test your knowledge. For all of our A Level Maths resources (including past papers), click the link below.

Explore our A Level Maths revision resources

Sign up for articles sent directly to your inbox

Receive news, articles and guides directly from our team of experts.

Related A Level Maths glossary terms

Series: A Level Maths Definition
Mark Curtis, Maths

Share this article

Logarithm - A Level Maths Definition

What is a logarithm?

Logarithm revision resources to ace your exams

Sign up for articles sent directly to your inbox

Reviewer: Mark Curtis

The examiner written revision resources that improve your grades 2x.