What is the syntax for LOG10 in Excel?

The syntax for LOG10 is: =LOG10(number)

What are common errors with LOG10?

#NUM! if number is zero or negative

How do I calculate pH using LOG10?

pH = -LOG10(hydrogen ion concentration). In Excel: =−LOG10(H_concentration). For example, if [H+] = 0.0001 M, then pH = -LOG10(0.0001) = 4. Remember pH is the negative log, so use the minus sign.

How do I find the order of magnitude of a number?

Use =FLOOR(LOG10(ABS(number)), 1) to get the order of magnitude. For 5,432 this returns 3 (thousands). For 0.0056 it returns -3 (thousandths). This tells you the power of 10 closest to your number.

What is the difference between LOG10 and LOG?

LOG10 always uses base 10. LOG uses base 10 by default but can accept any base as a second argument. LOG10(x) is identical to LOG(x) and LOG(x, 10). Use LOG10 when you specifically need base-10 for clarity.

Math & Trig

LOG10 Function in Excel

Returns the base-10 logarithm of a number.

Syntax

=LOG10(number)

Arguments

number (required): Positive number to find log of

Examples

=LOG10(100) - Log base 10 of 100 - Result: 2
=LOG10(1000) - Log base 10 of 1000 - Result: 3

LOG10 in reporting workflows

Use absolute references when copying formulas across rows.
For conditional totals see [SUMIF](/functions/sumif/) and [SUMIFS](/functions/sumifs/).
Filtered lists may need [SUBTOTAL](/functions/subtotal/) instead of SUM on visible cells only.

Common errors

#NUM! if number is zero or negative

Use cases

pH calculations
Decibels
Order of magnitude

Frequently asked questions

How do I calculate pH using LOG10? pH = -LOG10(hydrogen ion concentration). In Excel: =−LOG10(H_concentration). For example, if [H+] = 0.0001 M, then pH = -LOG10(0.0001) = 4. Remember pH is the negative log, so use the minus sign.
How do I find the order of magnitude of a number? Use =FLOOR(LOG10(ABS(number)), 1) to get the order of magnitude. For 5,432 this returns 3 (thousands). For 0.0056 it returns -3 (thousandths). This tells you the power of 10 closest to your number.
What is the difference between LOG10 and LOG? LOG10 always uses base 10. LOG uses base 10 by default but can accept any base as a second argument. LOG10(x) is identical to LOG(x) and LOG(x, 10). Use LOG10 when you specifically need base-10 for clarity.

Editorial review

Reviewed by Excel.Directory Editorial Team. Updated May 2026.