Syntax
LOG(number, [base])
| Parameter | Description |
|---|---|
| number | Parameter of the LOG function. |
| [base] | (Optional.) Parameter of the LOG function. |
Examples
Base 10 (default)
Formula
=LOG(1000)
Returns 3. 10^3 = 1000, so log base 10 of 1000 is 3.
Base 2 (binary)
Formula
=LOG(256, 2)
Returns 8. 2^8 = 256. Useful for computing: 256 bytes = 2^8, so you need 8 bits.
Custom base
Formula
=LOG(81, 3)
Returns 4. 3^4 = 81. The log base 3 of 81 is 4.
Common Errors
#NUM!
The number must be positive and the base must be positive and not equal to 1. =LOG(-5), =LOG(10, 0), or =LOG(10, 1) all return #NUM!.
#VALUE!
Non-numeric arguments return #VALUE!.
Tips
Default base is 10
=LOG(100) returns 2 because the base defaults to 10. Always specify the base explicitly if you mean something other than 10.
Bit counting
=CEILING(LOG(n, 2), 1) gives the number of bits needed to represent n values. Essential for computer science calculations.
pH scale
pH = -LOG(hydrogen_ion_concentration). The LOG function directly models the pH scale used in chemistry.
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