Relative Standard Deviation Calculator
RSD and coefficient of variation for replicate measurements.
Work out Relative Standard Deviation. RSD and coefficient of variation for replicate measurements. Says where the method stops being reliable.
Separate with commas or spaces. At least two.
Relative standard deviation
1.57%
mean 10.1, s = 0.1581, n = 5
RSD is the standard deviation as a percentage of the mean, which makes it comparable across methods measuring completely different quantities. Most analytical methods expect under 2% for replicate injections; chromatography peak areas are often held to 1%. This uses the sample standard deviation, dividing by n−1, because replicates are a sample of what the method would produce rather than the whole population. Note that RSD describes precision only — how repeatable the answer is. A method can be beautifully precise and consistently wrong, which is accuracy, and only a reference standard tests that.
How the Relative Standard Deviation Calculator works
Paste your replicate measurements and this returns the mean, sample standard deviation and RSD as a percentage. RSD is how analytical methods are compared, because expressing the spread relative to the mean makes it meaningful across techniques measuring completely different quantities.
Also known as: rsd calculator · coefficient of variation calculator · cv calculator for chemistry · precision calculator
Frequently asked questions
How do I calculate relative standard deviation?
Divide the sample standard deviation by the mean and multiply by 100. It is the coefficient of variation expressed as a percentage.
What is an acceptable RSD?
Under 2% for most analytical methods, and often under 1% for chromatographic peak areas from replicate injections. Trace analysis near the detection limit tolerates considerably more — 10% or 15% is not unusual.
Should I divide by n or n−1?
By n−1. Replicate measurements are a sample of what the method would produce if you kept measuring, not the entire population, and dividing by n underestimates the spread. This page uses n−1.
Does a low RSD mean the result is accurate?
No. RSD measures precision — how repeatable the answer is. A method can be extremely precise and consistently wrong through a calibration error. Only comparison against a reference standard tests accuracy.
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