Statistics
Math and statistics calculators with step-by-step formulas and worked examples for students and professionals.
Mean Calculator
Calculate the arithmetic, geometric and harmonic means of a data set, with formulas, a worked example, and guidance on when each mean is appropriate.
Median Calculator
Find the median, mode and range of a data set with worked examples. Handles even-sized lists and multiple modes, and explains median vs mean for skewed data.
Standard Deviation Calculator
Calculate sample and population standard deviation, variance and mean for any data set, with the n-1 vs n distinction explained and a worked example.
Probability Calculator
Calculate the probability of two independent events: both occurring, either occurring, neither occurring, and the complement — with formulas and examples.
Sample Size Calculator
Calculate the survey sample size you need using Cochran's formula with finite population correction, at 90%, 95% or 99% confidence and your margin of error.
Confidence Interval Calculator
Calculate a z-based confidence interval for a mean from the sample mean, standard deviation and size, with the margin of error and standard error shown.
Z-Score Calculator
Calculate a z-score from a value, mean and standard deviation, plus the normal-distribution percentile and the share of values above. Worked example inside.
Normal Distribution Calculator
Calculate normal-distribution probabilities — P(X < x), P(X > x) or P(x < X < b) — from a mean and standard deviation, with the z-score shown.
Binomial Distribution Calculator
Calculate binomial probabilities — exactly k, at most k, or at least k successes — from the number of trials and success probability, with mean and SD.
T-Test Calculator
Run a one-sample or two-sample (Welch's) t-test from summary statistics. Get the t-statistic, degrees of freedom and two-tailed p-value instantly.
Chi-Square Test Calculator
Run a chi-square goodness-of-fit test from observed and expected counts. Get the χ² statistic, degrees of freedom and p-value instantly.
Correlation Calculator
Calculate the Pearson correlation coefficient (r), R², and the least-squares regression line from paired x and y data. Free and instant.
Bayes' Theorem Calculator
Calculate a posterior probability with Bayes' theorem from a prior, sensitivity and false-positive rate. Classic base-rate example included.