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Quartile Deviation Calculator

Compute the semi-interquartile range and its coefficient, a spread measure that the extreme values cannot distort.

Related tools

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Quartile CalculatorCompute Q1, the median and Q3 with the position-by-position working, in the exclusive, inclusive and linear-interpolation methods.Average Deviation Calculator (mean absolute deviation)The average absolute deviation from the mean AND from the median — the median is the point that minimises it, which is worth seeing. Every |x − centre| is listed, and the standard deviation sits beside it for contrast: squaring makes SD react hard to a single outlier while the average deviation barely moves. The outlier preset is built to show exactly that.Sample Standard Deviation CalculatorCompute the sample standard deviation (n−1), variance, mean and detect outliers.Mean absolute deviation (MAD) calculatorCompute the mean absolute deviation of a data set around its mean.Median absolute deviation calculatorA robust measure of spread: the median of the absolute distances from the median. It shrugs off outliers where the standard deviation would blow up. Multiply by 1.4826 to estimate the standard deviation of clean data.Population standard deviation calculatorThe population standard deviation σ of a data set — how far the values spread from their mean when your data covers the whole group, dividing by N (not n−1). Enter the numbers and it returns σ, the variance σ², the mean and the count.Standard deviation calculatorCompute the standard deviation, variance and mean of a list.ANOVA Calculator (One-Way)Full one-way ANOVA table — SS, df, MS, F and p — plus η², ω² and Cohen's f, because a significant F on its own tells you nothing about how large the difference is. The equal-variance assumption is stated, not buried.

Quartile Deviation Calculator is free to use as often as you like, directly from this page. Its place is under Statistics & probability; Quartile Calculator and Average Deviation Calculator (mean absolute deviation) answer the questions closest to this one.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Quartile Deviation Calculator?

Compute the semi-interquartile range and its coefficient, a spread measure that the extreme values cannot distort.

When would I actually use this?

Summarising a dataset before drawing conclusions from it, checking whether a difference between two groups is real, and putting an interval around an estimate.

What is the most common mistake?

Reading a p-value as the probability that the hypothesis is wrong. It is the probability of seeing data at least this extreme if the null were true — a different statement, and a much weaker one.

How is Quartile Deviation Calculator different from Quartile Calculator?

They sit next to each other but answer different questions: Quartile Calculator is the one to open when you need it to compute Q1, the median and Q3 with the position-by-position working, in the exclusive, inclusive and linear-interpolation methods. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Average Deviation Calculator (mean absolute deviation) is the closest one after this: The average absolute deviation from the mean AND from the median — the median is the point that minimises it, which is worth seeing. Every |x − centre| is listed, and the standard deviation sits beside it for contrast: squaring makes SD react hard to a single outlier while the average deviation barely moves. The outlier preset is built to show exactly that.

What else is worth having open alongside it?

Sample Standard Deviation Calculator and Mean absolute deviation (MAD) calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Distributions and test statistics are computed from their standard definitions, not from a lookup table, so results carry more digits than a printed table would. The assumptions each test makes are stated with it.

Further reading

All guides →
How-toHow to Calculate Standard Deviation (Step by Step)Standard deviation measures how spread out your data is. Here's the formula, a worked example, and the difference between population and sample.ExplainerMean, Median and Mode: What's the Difference?Mean, median and mode all describe the 'middle' of your data — but answer different questions. Here's what each means, with examples and when to use which.ExplainerWhat Is a Percentile? The 90th Percentile ExplainedA percentile tells you where a value ranks within a group. Learn what the 90th percentile really means and why a percentile is not the same as a percentage.How-toHow to Calculate a Weighted AverageA weighted average gives some values more influence than others. Learn the Σ(w·x) / Σw formula with grade and portfolio examples you can follow step by step.How-toScientific Notation ExplainedScientific notation writes huge and tiny numbers as a value times a power of ten. Here's how to write it, read the exponent, and convert back.ExplainerA 1 % Drop Rate Does Not Mean One Hundred RunsAt 1 %, a hundred attempts give you 63.4 % — not certainty. Ninety per cent takes 230 attempts and ninety-nine takes 459, and more than a third of players are still empty-handed at a hundred.