Relative Risk Calculator

About this calculator

This calculator computes relative risk (RR), also called the risk ratio, from a 2×2 contingency table of exposed/unexposed groups and outcome/no-outcome counts: RR = [a/(a+b)] / [c/(c+d)], where a and b are the exposed group with and without the outcome, and c and d are the unexposed group with and without the outcome. An RR of 1 means no difference in risk between groups; RR of 2 means the exposed group has double the risk.

Relative risk is the standard measure reported in prospective cohort studies and randomized controlled trials to quantify how much an exposure — a drug, a risk factor, a behavior — changes the probability of an outcome, and it's distinct from odds ratio, which is used in case-control studies.

Epidemiologists and public health researchers analyzing cohort study data, clinicians interpreting drug trial results, and biostatistics students learning the difference between relative risk and odds ratio all use this calculation.