## Summary

The Excel LOG function returns the logarithm of a given number, using a supplied base. The base argument defaults to 10 if not supplied.

## Purpose

Get the logarithm of a number

The logarithm

## Arguments

• number - Number for which you want the logarithm.
• base - [optional] Base of the logarithm. Defaults to 10.

## Syntax

=LOG(number, [base])

## How to use

The LOG function returns the logarithm of a given number, using the provided base.

The LOG function takes two arguments, number and base. The value provided for number should be a positive real number. The base argument represents the base of the logarithm. Base is optional and defaults to 10 if not provided.

### Examples

The logarithm of 16 with base 2 (the power to which 2 must be raised to equal 16) is 4:

``````=LOG(16, 2) // returns 4
``````

The logarithm of 100 with base 10 (the power to which 10 must be raised to equal 100) is 2:

``````=LOG(100,10) // returns 2
``````

Because the base argument defaults to 10, the formulas below are equivalent:

``````=LOG(100,10) // returns 2
=LOG(100) // returns 2
``````

The LOG10 function also returns the base 10 logarithm of a number:

``````=LOG10(100) // returns 2
=LOG10(1000) // returns 3
``````

### Notes

• If number or base are not numeric, LOG returns #VALUE!
• The LOG10 function also returns the base 10 logarithm of a number.

Author

### Dave Bruns

Hi - I'm Dave Bruns, and I run Exceljet with my wife, Lisa. Our goal is to help you work faster in Excel. We create short videos, and clear examples of formulas, functions, pivot tables, conditional formatting, and charts.