Enter the weight you lifted and how many reps you completed to estimate your one-rep max using two established formulas.
How to Use the One Rep Max Calculator
Pick lb or kg as a label — the math is identical either way, so switching units doesn't convert your number, it just changes what's printed next to it — then enter the weight you lifted and how many reps you completed. Both the Epley and Brzycki estimates, plus their average, update with every keystroke.
Nobody needs to grind out an actual 1-rep max to know roughly what it is. Do a hard set of five, plug in the numbers, and two formulas developed decades apart, for different reasons, will each guess your ceiling from that single data point.
Why Two Formulas Instead of One
Epley: 1RM = Weight × (1 + Reps ÷ 30)
Brzycki: 1RM = Weight × 36 ÷ (37 − Reps)Boyd Epley built his version in 1985 while working as a strength coach in college football, aiming for something simple enough to use on a gym floor without a calculator handy. Matt Brzycki published his in a 1993 strength-and-conditioning journal, working from a different dataset and a slightly different mathematical shape. Neither is "the" correct formula — both are curve fits against real lifters, and real lifters don't all curve the same way.
The two tend to agree closely at low rep counts and drift apart as reps climb — Brzycki generally predicts a bit lower than Epley once you're past 8 or 10 reps, which is also exactly where both formulas get shakier in general. Above roughly 10 reps, fatigue and form breakdown distort the relationship between weight and true strength enough that neither equation is worth trusting much. Sets of 3–6 reps give the most reliable estimate here.
Percentage-based programming is the actual reason to bother with this calculator at all — a program written as "work up to 3x5 at 75% of 1RM" only makes sense once there's a 1RM figure, estimated or otherwise, to calculate that percentage from. None of this replaces an actual tested max — these are estimates from submaximal data, run through math, nothing more.
Not a number to load on the bar. This is an estimate from a submaximal lift, not a tested 1-rep max. Use it for programming percentages — working at 80% of your estimated 1RM, for example — not as a target to attempt directly. If you do want to test a true max, work up to it gradually and ideally with a spotter or trainer present.