🏋️ One-Rep Max Calculator
Enter the weight and reps from a recent hard set to estimate your one-rep max with the Epley and Brzycki formulas, plus a percentage table for programming your working sets.
🏋️ Estimate Your One-Rep Max
What is a One-Rep Max Calculator?
It estimates the heaviest weight you could lift for a single rep, based on a set you took close to failure at a higher rep count. Rather than testing a true max — which carries real injury risk — you enter the weight and reps from a recent hard set, and it applies the Epley and Brzycki formulas to project what a single rep at that effort would look like.
Use the estimate to program training percentages, track strength progress over time, or plan a peaking block without needing to attempt a maximal lift every few weeks. Warm up thoroughly, use proper form, and treat the number as a guide — this is a general fitness estimate, not medical advice.
❓ Frequently Asked Questions
How does the one-rep max calculator work?
Enter the weight you lifted and the number of reps you completed on a set taken close to failure. It runs that through two well-known formulas — Epley and Brzycki — averages them, and builds a percentage table so you know what to load for a given percentage of your estimated max.
What are the Epley and Brzycki formulas?
The Epley formula estimates 1RM as weight × (1 + reps/30). The Brzycki formula estimates it as weight × 36 / (37 − reps). They tend to agree closely for lower rep counts and diverge more as reps climb, which is why this calculator averages the two for a more balanced estimate.
Why does accuracy drop at higher rep counts?
Both formulas assume a fairly linear relationship between reps and strength loss, which holds reasonably well up to around 10–12 reps. Beyond that, muscular endurance and fatigue effects distort the estimate, so this calculator caps input at 20 reps and any estimate from very high-rep sets should be treated as a rough guide only.
How do I use the percentage table for training?
Strength programs are often written as a percentage of your one-rep max — for example, 5 sets of 5 at 80%, or a heavy single at 95%. Once you have an estimated max, multiply it by the target percentage (or read it straight off the table) to know what to load on the bar.