1RM Calculator

Your one rep max is the most you can lift for a single rep, and it is the number most strength programs are built around. You do not have to actually max out to know it, which is good, because true one-rep attempts are risky and tiring. The calculator above estimates your 1RM from any set you have already done.

How the estimate works

Enter a weight and the number of reps you got with it. The calculator averages two well-established formulas, Epley and Brzycki, which both model the relationship between reps and load. From there it builds a full percentage table so you can see what your working weights should be across the rep ranges you train in.

The estimate is most accurate when you tested with a hard, near-maximal set of ten reps or fewer. The further past ten you go, the more the relationship between reps and max drifts, because high-rep sets are limited as much by muscular endurance and fatigue as by raw strength.

Why the percentages matter

A 1RM is only useful because of what it lets you program. Most strength work is prescribed as a percentage of it: heavy triples at 90%, working sets of five around 80%, higher-rep hypertrophy work down at 70%. Knowing your max lets you pick loads that match the goal of the session instead of guessing.

The table above gives you the common percentages and the rough rep ranges each one supports. Use it to set your top sets and back-off sets without doing the math each time.

A note on safety and honesty

Estimate from clean reps with good form, not grinding ugly singles. A rep that turns into a near-miss inflates the estimate and sets your future loads too high. Re-estimate every few weeks as you get stronger, ideally from a hard set in the three to six rep range, which sits in the sweet spot for accuracy.

For how to actually program those percentages into a week that builds strength alongside your other training, read the strength training guides.