LOG10 Function in Excel

The LOG10 function in Excel returns the base-10 logarithm of a positive number.

The result is the exponent needed to raise 10 to that number. This makes LOG10 useful for comparing orders of magnitude or transforming values spanning a wide range.

Values between zero and one return negative logarithms. Zero and negative inputs are outside the function’s real-number domain.

In this article, I’ll show you how to transform response times, convert power ratios to decibels, and measure changes in orders of ten.

LOG10 Function Syntax in Excel

LOG10 needs one positive real number:

=LOG10(number)
  • number is the required positive real number whose base-10 logarithm you want.

When to Use LOG10 Function

  • Find the exponent that raises 10 to a given positive value.
  • Compress a wide range of positive values into a base-10 scale.
  • Calculate a power ratio in decibels.
  • Measure a change in orders of magnitude between two positive values.

Example 1: Find Powers of Ten With LOG10

Let’s start with the meaning of the result.

Below is a column of positive values, including values smaller than 1. Column B is ready for the base-10 logarithms.

LOG10 example 1: dataset and empty result cells

I want to find the exponent of 10 for every value in column A.

Here is the formula:

=LOG10(A2:A8)
LOG10 example 1: =LOG10(A2:A8)

The formula spills results from B2 through B8. For example, LOG10 of 0.01 is -2 because 10 raised to -2 equals 0.01.

Likewise, 10 returns 1, 100 returns 2, and 100,000 returns 5. The result is always the exponent, not a percentage or a scaled copy of the original number.

In Excel 2019 and earlier, enter =LOG10(A2) in B2 and fill it down. Keep the cells below a spilling formula empty in newer Excel, or Excel returns #SPILL!.

Pro Tip: LOG(A2:A8) also uses base 10 when its optional base is omitted. LOG10 is clearer when base 10 is exactly what you mean.

Example 2: Log Transform Response Times

Here is a practical use for a wide numeric range.

Below are service queues and their response times in milliseconds. The response times range from 18 to 3,400 ms.

LOG10 example 2: dataset and empty result cells

I want a log-transformed response-time column that makes the scale easier to compare.

Here is the formula:

=LOG10(B2:B7)
LOG10 example 2: =LOG10(B2:B7)

The formula spills the transformed values into C2:C7. The 18 ms response time becomes 1.255273, while 3,400 ms becomes 3.531479.

This does not make the long response time disappear. It changes the scale so multiplicative differences take less space, which can help when you compare a very wide positive range.

Example 3: Convert Power Ratios to Decibels

LOG10 is also part of the standard power-ratio decibel calculation.

Below are power ratios for several system pairs. Column C will show the level difference in decibels.

LOG10 example 3: dataset and empty result cells

I want to convert each power ratio to a decibel difference.

Here is the formula:

=10*LOG10(B2:B7)
LOG10 example 3: =10*LOG10(B2:B7)

The formula returns -10 dB for a 0.1 ratio, 0 dB for a ratio of 1, and 20 dB for a ratio of 100.

A ratio below 1 produces a negative result because it represents a lower power level. This formula is for power ratios. Other decibel calculations can use a different multiplier.

Example 4: Measure an Orders-of-Ten Change

You can also compare a starting value with a target value.

Below are starting and target values for several business segments. Column D will show the change in base-10 orders of magnitude.

LOG10 example 4: dataset and empty result cells

I want to calculate how many powers of 10 each target has increased or decreased from its starting value.

Here is the formula:

=LOG10(C2:C7/B2:B7)
LOG10 example 4: =LOG10(C2:C7/B2:B7)

North changes from 25 to 250, so its result is 1. That target is one order of magnitude larger than its starting value.

East changes from 400 to 40, so its result is -1. A negative result means the target is smaller by that number of base-10 orders.

Example 5: Handle Zero, Negative, and Text Inputs

LOG10 has a firm input boundary.

Below are valid, zero, negative, decimal, and text inputs. Column B keeps the original LOG10 result visible, while column C adds a reader-friendly message.

LOG10 example 5: dataset and empty result cells

I want to see the native errors and show a clear message for invalid inputs.

Here is the raw LOG10 formula:

=LOG10(A2:A7)
LOG10 example 5: =LOG10(A2:A7)

Zero and -25 return #NUM! because they are not positive real numbers. The text value returns #VALUE!.

Here is the formula with an error message:

=IFERROR(LOG10(A2:A7),"Enter a positive number")
LOG10 example 5: =IFERROR(LOG10(A2:A7),"Enter a positive number")

The valid values stay as their LOG10 results. The invalid values show the message instead.

Use this pattern when a worksheet needs a clear user-facing result. Keep the raw formula nearby while you are checking imported data, because it tells you whether the issue is #NUM! or #VALUE!.

Tips & Common Mistakes

  • LOG10 accepts positive real numbers only. Zero and negative numbers return #NUM!.
  • Use LOG when you need a base other than 10.
  • Use LN for natural logarithms, which use the base e.
  • Use =10^x to reverse a base-10 logarithm. See this guide to calculating antilog in Excel for examples.
  • Do not use a power-ratio decibel formula for a voltage or amplitude ratio. The multiplier depends on the quantity you are measuring.

I have shown you how to use LOG10 for powers of ten, transformed values, ratios, and input checks.

I hope you found this article helpful.

List of All Excel Functions