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Logarithm - A Level Maths Definition

Reviewed by: Mark Curtis

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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 subscript a open parentheses b close parentheses equals 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 subscript 2 open parentheses 8 close parentheses represents the power of 2 that gives you 8. This is 3 (because 2 cubed equals 8) so

log subscript 2 open parentheses 8 close parentheses equals 3

If a log is written without a base in A Level, i.e. as log open parentheses... close parentheses, it means log of base 10, log subscript 10 open parentheses... close parentheses. If a log is written as ln open parentheses... close parentheses, it means log of base e (called a natural logarithm).

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Mark Curtis

Reviewer: Mark Curtis

Expertise: Maths Content Creator

Mark graduated twice from the University of Oxford: once in 2009 with a First in Mathematics, then again in 2013 with a PhD (DPhil) in Mathematics. He has had nine successful years as a secondary school teacher, specialising in A-Level Further Maths and running extension classes for Oxbridge Maths applicants. Alongside his teaching, he has written five internal textbooks, introduced new spiralling school curriculums and trained other Maths teachers through outreach programmes.

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