One Rep Max Calculator

Estimated 1RM from a lifted weight and rep count (Epley & Brzycki formulas)

Estimating a one-rep max (1RM) — the maximum weight that could theoretically be lifted for a single repetition — from a lighter weight lifted for multiple reps uses established formulas (Epley and Brzycki are the two most common) rather than requiring an actual maximal single-rep attempt, which carries real injury risk especially for less experienced lifters.

Why formula-based estimation exists, and why two formulas can disagree

Both the Epley and Brzycki formulas estimate 1RM from a submaximal weight-and-reps combination, but they use different underlying mathematical relationships between reps performed and estimated maximum strength — this means the same lifted weight and rep count can produce a slightly different 1RM estimate depending on which formula is used, and neither formula is universally more accurate across every rep range; each tends to perform somewhat differently at very low versus higher rep counts. These formulas are also most reliable within a moderate rep range (roughly single digits to low double digits) — extrapolating from a very high rep count (20+ reps) to estimate 1RM introduces substantially more estimation error than extrapolating from a lower, more moderate rep count.

A worked example

The identical weight-and-reps input run through the Epley formula versus the Brzycki formula can produce two slightly different 1RM estimates — neither is definitively "more correct" in isolation, and for practical training purposes, treating the estimate as a reasonable approximate range rather than an exact number (and testing periodically with lower-rep, more accurate-estimate sets) is more useful than fixating on a single precise figure from either formula.

How this connects to your other health and fitness calculations

1RM estimates are commonly used to set percentage-based training loads for a program — a related but separate calculation from the raw estimate itself. For overall daily energy needs to support a training program, the Calorie/TDEE Calculator and Protein Calculator cover the nutritional side of training that this strength-estimate calculator doesn't address.

Common mistakes

Treating a formula-estimated 1RM as a precise, load-bearing-tested number rather than a reasonable estimate is a common overreach — using an estimated 1RM to set training percentages is standard and useful practice, but attempting an actual maximal single-rep lift purely to "verify" the estimate carries real injury risk that most training programs don't actually require taking.