One Rep Max (1RM) Calculator

What Is a One-Rep Max?

Your one-rep max, or 1RM, is the maximum amount of weight you can lift for a single complete repetition of an exercise with correct form. It's the standard reference point strength coaches and lifters use to plan training percentages, compare progress over time, and set realistic goals for programs built around squats, deadlifts, bench press, or overhead press.

Actually testing a true 1RM means loading a bar until you fail, which carries real injury risk and isn't something most lifters need to do often. Instead, you can estimate it from a lighter set you've already performed — for example, a set of 5 reps you completed with good form — using a set of well-tested strength-prediction formulas.

How to Use This Calculator

Enter the weight you lifted, choose kg or lb, and enter how many clean reps you completed with that weight (up to 12). Click "Calculate 1RM" and you'll get an estimated one-rep max, along with a breakdown showing how each individual formula scored it and a table of common training percentages based on that estimate.

For the most accurate estimate, use a set taken close to failure — the last rep should have been genuinely hard, not one you could have repeated five more times.

How We Calculate Your Estimated 1RM

No single formula predicts 1RM perfectly for every lifter, rep range, or exercise, so this calculator averages four formulas that are widely used in strength training: Epley, Brzycki, Lander, and Lombardi. Each one models the relationship between weight and reps slightly differently, and averaging them smooths out the quirks any one formula has at the edges of its range.

These formulas are most accurate for sets of 1 to 10 reps performed close to failure. Above 10-12 reps, the estimate becomes noticeably less reliable, which is why the calculator caps input at 12 reps.

A Few Notes on Accuracy and Safety

This tool gives a mathematical estimate, not a guarantee — individual factors like lifting experience, exercise choice, and fatigue on the day can shift your real 1RM up or down from the prediction. Treat the result as a solid planning number rather than an exact figure.

If you do want to test your actual 1RM, warm up thoroughly, increase weight gradually, and use a spotter or safety equipment for any lift where failing under the bar would be dangerous.