About

1rm.dev is a fitness calculator for one-rep max estimates, working loads, plate math, points scores, and a few field tests. Julien Kollmann publishes it from Passau, Germany. The same formulas run in the browser, on the public HTTP API, and on the MCP server, so a person and an agent receive the same number from the same equation.

A one-rep max is the heaviest load you could lift for a single repetition. The calculators estimate that load from a set you already completed: the weight, the repetitions, and an optional RPE or reps in reserve. The default formula is Epley. Every method has a cited card with the equation, the year, and the source. There is no account and no API key. Defaults are kilograms and Epley unless you choose otherwise.

These tools are estimates from published formulas or common gym practice. They are not a training plan, a coaching service, or medical advice. The German statutory notice, including the operator address, is on the Impressum page at /impressum. The English privacy note is at /privacy. Questions go to hi@julien1k.com.