# Statistics & Probability calculators

> Descriptive statistics, z-scores, normal and binomial probability, confidence intervals, sample size, regression.

14 calculators. HTML index: https://tttkmbb.com/statistics · JSON: https://tttkmbb.com/api/v1/calculators?category=statistics

- [Descriptive Statistics Calculator](https://tttkmbb.com/statistics/descriptive-statistics.md): Computes summary statistics for a list of numbers: count, sum, mean, median, mode, range, sample and population variance and standard deviation, standard error, coefficient of variation, quartiles (linear interpolation) and skewness. Tool: `calculate_descriptive_statistics`.
- [Z-Score Calculator](https://tttkmbb.com/statistics/z-score.md): Standardises a value against a mean and standard deviation (z = (x − μ) / σ) and reports the corresponding percentile and tail probabilities under the normal distribution. Tool: `calculate_z_score`.
- [Normal Distribution Calculator](https://tttkmbb.com/statistics/normal-distribution.md): Computes cumulative probabilities P(X < x), P(X > x) and P(x < X < x2) and the density for a normal (Gaussian) distribution with a given mean and standard deviation. Tool: `calculate_normal_distribution_probability`.
- [Confidence Interval Calculator](https://tttkmbb.com/statistics/confidence-interval.md): Computes a confidence interval for a population mean from the sample mean, standard deviation and sample size using the normal (z) critical value: mean ± z · s / √n. Tool: `calculate_confidence_interval`.
- [Sample Size Calculator](https://tttkmbb.com/statistics/sample-size.md): Computes the number of respondents needed to estimate a population proportion within a given margin of error at a given confidence level (Cochran's formula), with an optional finite population correction. Tool: `calculate_sample_size`.
- [Margin of Error Calculator](https://tttkmbb.com/statistics/margin-of-error.md): Computes the margin of error (half-width of the confidence interval) of a sample proportion from the sample size, confidence level and observed percentage, with an optional finite population correction. Tool: `calculate_margin_of_error`.
- [Binomial Distribution Calculator](https://tttkmbb.com/statistics/binomial-distribution.md): Computes the probability of exactly, at most, at least, fewer than or more than k successes in n independent trials with success probability p, plus the mean, variance and standard deviation of the distribution. Tool: `calculate_binomial_probability`.
- [Poisson Distribution Calculator](https://tttkmbb.com/statistics/poisson-distribution.md): Computes the probability of exactly, at most, at least, fewer than or more than k events when events occur independently at a constant average rate λ per interval, plus the mean, variance and standard deviation. Tool: `calculate_poisson_probability`.
- [Probability of Two Events Calculator](https://tttkmbb.com/statistics/probability-of-events.md): Combines the probabilities of two events A and B that are either independent or mutually exclusive into the probabilities of both, at least one, exactly one, one but not the other, and neither occurring. Tool: `calculate_event_probabilities`.
- [Correlation Coefficient Calculator](https://tttkmbb.com/statistics/correlation.md): Computes the Pearson product-moment correlation coefficient r, the coefficient of determination r², and the sample covariance for two paired lists of numbers, with a strength/direction interpretation. Tool: `calculate_correlation`.
- [Linear Regression Calculator](https://tttkmbb.com/statistics/linear-regression.md): Fits an ordinary least-squares line to paired (x, y) data and returns the slope, intercept, equation, Pearson r, R², the standard error of the estimate and an optional prediction for a new x. Tool: `calculate_linear_regression`.
- [Weighted Average Calculator](https://tttkmbb.com/statistics/weighted-average.md): Computes the weighted arithmetic mean Σ(w·x) / Σw of a list of values and a matching list of weights, along with the total weight and the unweighted mean for comparison. Tool: `calculate_weighted_average`.
- [Percentile Calculator](https://tttkmbb.com/statistics/percentile.md): For a list of numbers, computes the value at a given percentile (linear interpolation, as in Excel PERCENTILE.INC) and/or the percentile rank of a given value (percentage of values below it, counting ties as half). Tool: `calculate_percentile`.
- [Expected Value Calculator](https://tttkmbb.com/statistics/expected-value.md): Computes the expected value E[X] = Σ x·p(x), the variance and the standard deviation of a discrete random variable from its list of outcomes and their probabilities. Tool: `calculate_expected_value`.