Sample size, margin of error, standard error, and accuracy calculators. Browse our free sampling tools below — all calculators are instant, accurate, and require no sign-up.
Constant of Proportionality Calculator — Find the constant of proportionality k from data pairs. Supports direct, inverse, squared, square root, and custom power models with R², residuals, and fit analysis.
Accuracy Calculator — Calculate accuracy, precision, recall, F1, MCC from a confusion matrix. Also computes measurement error metrics (MAE, RMSE, MAPE) and simple proportion accuracy with confidence intervals.
Margin of Error Calculator — Calculate margin of error from sample data or find required sample size for a desired MOE. Supports proportions and means with finite population correction.
Sampling Distribution of Sample Proportion Calculator — Explore the sampling distribution of p̂. Calculate mean, standard error, probabilities, and quantiles. Visualize the bell curve with normal approximation conditions.
Sampling Error Calculator — Calculate sampling error (standard error and margin of error) for proportions and means. Includes finite population correction, error decomposition, and sample size comparison.
Sensitivity & Specificity Calculator — Calculate sensitivity, specificity, PPV, NPV, likelihood ratios, and Youden's J from a confusion matrix. Includes PPV/NPV table at different prevalence levels.
Specificity Calculator — Calculate specificity (true negative rate) from TP, FP, FN, TN. Includes false positive rate, confidence interval, prevalence-adjusted PPV table, and diagnostic metrics.
Standard Error Calculator — Calculate standard error for means, proportions, differences, or raw data. Includes margin of error, finite population correction, and SE vs sample size comparison.