LOG10 Function in Microsoft Excel: Examples, Pitfalls & Compatibility
LOG10 in Microsoft Excel: calculate a base-10 logarithm for positive inputs without an optional-base argument. Includes worked examples and application-specific cautions.
Verification status: Official documentation referenced; example outcomes independently reasoned or arithmetically checked where stated. Not executed in Microsoft Excel. How formula examples are checked
Quick answer: Use LOG10 in Microsoft Excel to calculate a base-10 logarithm for positive inputs without an optional-base argument. The official LOG10 reference is the source for the function definition and platform-specific rules described below.
Syntax and arguments
=LOG10(number)
number (required): A strictly positive real number whose base-10 exponent is required.
Examples use English function names, comma argument separators and decimal points. Adapt formula separators to your workbook settings, not punctuation inside quoted text.
When to use it
Use LOG10 for decimal orders of magnitude or a model explicitly defined with base 10. Use LN for a natural logarithm. Do not confuse a logarithm with rounding a number to a certain number of significant figures.
Three worked examples
Each example is independent. Where input cells are listed, enter those values first; otherwise the formula is self-contained. Expected outputs are independently checked calculations or documented error expectations, not captured results from Microsoft Excel.
Example 1: Read an exact decimal scale
=LOG10(1000000)
Expected result: 6.
The value is 10 to the power 6.
Example 2: Read a reciprocal decimal scale
=LOG10(0.001)
Expected result: -3.
The value is 10 to the power -3. The negative output is valid.
Example 3: Transform a non-power value
=ROUND(LOG10(250),6)
Expected result: 2.39794.
The exponent lies between 2 and 3 because 250 lies between 100 and 1000. Reporting six decimals may display a trailing zero.
Put it to work safely
Keep the original value beside its logarithm and state the base in the column heading. Test powers of ten, a positive fraction and a non-power value before analysing a larger series. A ratio-based comparison can be easier to interpret than the logarithm of a dimensioned quantity; whatever model is chosen should have a clear meaning.
Common mistakes and fixes
A small positive value has a negative answer. That is correct for values strictly between zero and one. The input is still inside the positive-real domain.
A zero or negative input is present. This real-valued logarithm is not defined for those inputs. Flag them rather than silently changing the input.
A noninteger output is mistaken for a digit count. LOG10 returns an exponent. A whole-number digit-count rule needs additional conditions and is not the same operation.
Microsoft Excel-specific notes
Microsoft defines LOG10 with one positive-real argument. An explicit base-10 function can make a long formula easier to read than relying on LOG’s omitted default. See the vendor reference for the current definition.
Excel and Google Sheets comparison
The documented base and positive-real domain align. The six-decimal example is an independently calculated expectation, not evidence of identical internal precision or error coercion.
Compare the LOG10 guide for Google Sheets and its official documentation. Having a guide in both libraries establishes two documented references, not a certificate of identical behavior across releases, locales or file conversions.
Related guides
LOG, LN, POWER, ROUND · All Microsoft Excel functions.
Evidence and testing scope
Editorial verification: Official references retrieved on 2026-10-12. The three worked cases are included in this release’s reproducible Python checking suite. It checks the stated arithmetic, calendar or text model and the expected documented error classification; it is not the Microsoft Excel calculation engine. No native application run, UI screenshot, maximum-size benchmark or cross-version certification is claimed. Review the editorial testing standards before relying on a formula in a critical workbook.