LOG Function
Returns the logarithm of a number to a given base (default 10).
Syntax
Parameters
| Parameter | Description | Required |
|---|---|---|
| number | The positive real number for which you want the logarithm. | Required |
| base | The base of the logarithm. Optional; defaults to 10 if omitted. | Optional |
Basic Example
Base-10 log of 1000
=LOG(1000)With the base omitted, LOG uses 10; 10³ = 1000, so the result is 3.
Advanced Examples
Example 1: Logarithm in base 2
Measuring bits or orders of magnitude.Specify base 2 explicitly.
=LOG(8, 2)Example 2: Base-10 explicitly
Clarity in a formula.Pass 10 as the base.
=LOG(100, 10)How LOG Works
LOG computes log_base(number), the exponent to which the base must be raised to equal the number. When base is omitted it defaults to 10. Mathematically LOG(n, b) = LN(n) / LN(b).
Important Notes & Limitations
The number must be positive; otherwise #NUM!.
The base must be positive and not equal to 1; base 1 returns an error.
Omitting the base yields base 10, which some users confuse with natural log.
Common Errors & Fixes
#NUM!Number is 0/negative, or base is invalid (e.g. 1 or negative).Fix: Use a positive number and a positive base other than 1.
#VALUE!Non-numeric argument.Fix: Supply numeric values.
Download Practice File
LOG
logPractice LOG with Real Data
Download a sample CSV file with pre-populated data and practice exercises for the LOG function. Works in both Excel and Google Sheets.
File format: CSV (comma-separated values) - opens in Excel, Google Sheets, and all spreadsheet apps