RSD Calculator (Relative Standard Deviation)

Calculate Relative Standard Deviation (RSD) and Coefficient of Variation (CV) from a data set.

Last updated: 10/27/2026

This RSD calculator finds the relative standard deviation, often written %RSD, of a list of numbers. Paste or type your values and it returns the RSD, the standard deviation and the mean. RSD is the same measure as the coefficient of variation (CV), expressed as a percentage. It shows how large the spread is compared with the average, so it is often used to check the precision of repeated lab measurements.

Calculator Inputs

Data Points*

Enter numbers separated by commas or spaces

Results

Enter values above to see your results

How to use this calculator

Enter at least two numbers, separated by commas, spaces or new lines. You can paste a column straight from a spreadsheet.
The main result uses the sample standard deviation, which is what most labs and spreadsheets use for replicate measurements.
If your numbers are the whole population rather than a sample, use the population RSD in the breakdown instead.

How the calculation works

RSD (%) = (s / x̄) × 100, where s is the standard deviation and x̄ is the mean.

Sample standard deviation: s = √( Σ(x − x̄)² / (n − 1) ).

Population standard deviation: σ = √( Σ(x − x̄)² / n ).

The RSD is shown as a positive number. It cannot be calculated when the mean is zero.

Worked example

Dataset: 10, 12, 11

Mean:(10 + 12 + 11) / 3= 11

Squared deviations:(10 − 11)² + (12 − 11)² + (11 − 11)²= 2

Sample standard deviation:√(2 / (3 − 1))= 1

RSD:(1 / 11) × 100= 9.09%

Population RSD:(√(2 / 3) / 11) × 100= 7.42%

Five replicate measurements: 98.2, 99.1, 100.4, 99.6, 98.9

Mean:496.2 / 5= 99.24

Squared deviations:Σ(x − 99.24)²= 2.692

Sample standard deviation:√(2.692 / 4)= 0.8204

RSD:(0.8204 / 99.24) × 100= 0.83%

Tips & Best Practices

•A lower RSD indicates better precision (data points are closer to the mean).
•RSD is useful for comparing the spread of two different datasets with different means.
•In Excel or Google Sheets, sample %RSD is =STDEV.S(range)/AVERAGE(range)*100.

Frequently Asked Questions

What is the RSD formula?

RSD = (Standard Deviation / Mean) × 100%.

How do I calculate RSD by hand?

Find the mean, subtract it from each value and square the results, add those squares, divide by n − 1, and take the square root to get the standard deviation. Divide that by the mean and multiply by 100.

Should I use sample or population standard deviation?

Use the sample standard deviation (n − 1) when your values are a sample, such as repeated measurements of one solution. Use the population version (n) only when you have every value in the group. The breakdown shows both.