Purpose
Return value
Syntax
=LOG(number,[base])
- number - Number for which you want the logarithm.
- base - [optional] Base of the logarithm. Defaults to 10.
Using the LOG function
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.
Purpose
Return value
Syntax
=LOG10(number)
- number - The positive number for which you want the base-10 logarithm.
Using the LOG10 function
LOG10 returns the base-10 logarithm of a number. In simple terms, it answers the question: “10 raised to what power gives me this number?” The table below shows how LOG10 works and how it is related to raising 10 to a specific power:
| Number | LOG10 | Because |
|---|---|---|
| 1000 | 3 | 10³ = 1000 |
| 100 | 2 | 10² = 100 |
| 10 | 1 | 10¹ = 10 |
| 1 | 0 | 10⁰ = 1 |
| 0.1 | -1 | 10⁻¹ = 0.1 |
| 0.01 | -2 | 10⁻² = 0.01 |
For numbers that aren’t exact powers of 10, LOG10 will return get decimals:
| Number | LOG10 |
|---|---|
| 50 | 1.699 |
| 3697 | 3.568 |
| 0.3697 | -0.432 |
To use Excel’s LOG10 function, just supply a number:
=LOG10(1000) // returns 3
=LOG10(100) // returns 2
=LOG10(10) // returns 1
=LOG10(1) // returns 0
=LOG10(0.1) // returns -1
=LOG10(0.01) // returns -2
