Risk Ratio (Relative Risk) Calculator

About this calculator

The risk ratio, also called relative risk, compares the probability of an event between two groups: it is the risk in the exposed group (events divided by total people in that group) divided by the risk in the unexposed or control group. A risk ratio of 1.0 means no difference between groups, a value above 1.0 means the exposed group is more likely to experience the event, and a value below 1.0 means the exposure appears protective.

Epidemiologists and clinical researchers use risk ratios in cohort studies and randomized controlled trials, where the absolute number of people at risk from the outset is known — this distinguishes it from the odds ratio, which is used instead in case-control studies where the group sizes are chosen by the researcher rather than reflecting the true population at risk.

This calculator takes the event count and group total for both the exposed and control groups and returns the risk ratio, letting you quantify how much more or less likely an outcome is in one group compared to the other.