Statistics & Probability Calculators
Summary statistics, spread, weighted averages, counting, probability and distributions.
Calculators
- Mean, Median and Mode Calculator
Mean, median, mode, range and quartiles for a data list, with the quartile method stated.
- Standard Deviation Calculator
Sample or population variance and standard deviation, step by step.
- Weighted Average Calculator
Average of values with weights, such as grades or blended rates.
- Permutation and Combination Calculator
Exact counts of arrangements and selections, with or without repetition.
- Probability Calculator
And, or, not and conditional probability for independent or dependent events.
- Binomial Distribution Calculator
Exact and cumulative binomial probabilities with the full distribution table.
- Normal Distribution and Z-Score Calculator
Normal probabilities, z-scores and percentiles, with accuracy limits stated.
Which statistics or probability calculator to use
The tools here split into two groups: summarizing data you already have, and working out chances from a model of how the data arise.
- What does this data set look like?
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Mean, Median and Mode Calculator
Mean, median, mode and quartiles, with the quartile method stated and outliers flagged by the 1.5 × IQR rule.
- How spread out are the values?
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Sample or population standard deviation and variance, with a table of deviations from the mean.
- An average where some values count more?
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Weighted mean for grades, portfolios or prices, with the weights shown as shares of the total.
- How many arrangements or selections?
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Permutation and Combination Calculator
Counts with or without order and repetition, exact even when the answer runs to thousands of digits.
- What are the chances?
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Probability Calculator Binomial Distribution Calculator Normal Distribution and Z-Score Calculator
Combined events, successes in a fixed number of independent trials, or areas under a bell curve with z-scores and percentiles.
Have these to hand
- The raw values, pasted from a spreadsheet column or separated by commas or spaces.
- Whether the values cover the whole population or are a sample from it.
- For a probability model, the number of trials and the chance of success on each.
Mistakes that change the answer
- Using the population formula on a sample, which understates the standard deviation.
- Treating events as independent when one affects the other.
- Assuming a skewed data set is normal just because its mean and standard deviation are known.
- Counting ordered arrangements when order does not matter, which multiplies the count.
Related guides
- Mean, median or mode? How to choose a summary statistic
How to pick the center and spread that describe your data fairly, with worked numbers and a side-by-side of the quartile rules that different tools use.
- Common percentage mistakes and how to avoid them
Six percentage slips that produce confident wrong answers, from percentage points to negative starting values, each worked with example numbers you can check.
- Solving triangles: which rule to use, and the SSA ambiguous case
A table for choosing the law of sines or the law of cosines, a worked SSA example with two valid answers, and the step-order and rounding traps that make hand-solved triangles go wrong.
- How to measure a room for square footage and volume
Measure, convert inches to decimal feet, split odd shapes into rectangles, then multiply and convert with a squared or cubed factor. Worked with an L-shaped room, a concrete pad and a water tank.
- How much extra flooring, tile, paint and concrete to buy
Published rules of thumb for overage by material and layout, what each one covers, and worked examples that apply the allowance first and round up to whole boxes, cans and bags last.
- Margin vs. markup: formulas, conversion chart and discounts
Margin and markup divide the same profit by different numbers. How to convert one to the other, set a price for a target margin, and work out what a discount really costs.