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LOG Function
Summary
The Excel LOG function calculates the logarithm of a specified number using a customizable base. When no base is provided, it defaults to base 10, making it perfect for logarithmic calculations in finance, science, and data analysis.
Syntax
LOG(number, [base])Parameters
| Parameter | Type | Required | Description |
|---|---|---|---|
| number | Number |
Yes | The positive real number (>0) for which you want the logarithm |
| base | Number |
No | The base of the logarithm. Defaults to 10 if omitted |
Using the LOG Function
Use LOG for mathematical computations involving exponents, financial modeling (compound interest), scientific data analysis, and scaling large datasets. It's particularly useful when you need logarithms beyond the fixed base-10 (LOG10) or natural log (LN) functions.
Common LOG Examples
Base 10 Logarithm (Default)
=LOG(10)Returns 1, as 10^1 = 10 (base defaults to 10)
Binary Logarithm
=LOG(8,2)Returns 3, as 2^3 = 8
Natural Logarithm (base e)
=LOG(86,2.7182818)Returns approximately 4.454, as e^4.454 ≈ 86
Frequently Asked Questions
Common Errors and Solutions
#NUM!
Cause: Number ≤ 0 or invalid base
Solution: Ensure number > 0 and base > 0, base ≠ 1
#VALUE!
Cause: Non-numeric arguments
Solution: Use numeric values only
Notes
- Number must be greater than 0
- Base must be positive and not equal to 1
- For natural log, use LN() or LOG(number,e)
- Common bases: 2 (binary), 10 (common), e (2.71828 natural)
Compatibility
Available in: Excel 2007, Excel 2010, Excel 2013, Excel 2016, Excel 2019, Excel 2021, Excel 365
Not available in:
Content last reviewed: December 11, 2025
Update frequency: As needed
Excel versions tested: Excel 2007+