One-rep max calculator
Enter a set you actually completed and this estimates the most you could lift once, using the two formulas everybody uses. It runs in your browser — nothing you type is sent anywhere.
| Percent | Weight | Reps you should get |
|---|
How the estimate works
Both formulas are curve fits to the same observation: the more reps you can do with
a weight, the further that weight sits below your maximum. Epley works out to
weight × (1 + reps ÷ 30). Brzycki works out to
weight × 36 ÷ (37 − reps). Neither knows anything about you.
That matters, because rep performance at a given percentage varies enormously between people and between lifts. Some lifters grind out twelve reps at 75 percent; others stop at seven. If you have been training a while, your own history is a better predictor than either formula, which is exactly why it is worth logging.
How to use the percentage table
Most strength programs are written in percentages of a maximum — five sets of three at 80 percent, say. The table above turns the estimate into the weights you would actually load. Treat the top rows as a ceiling rather than a target: if 90 percent feels like a grind on the day, run the session at 85 and log what you did.
A better number than an estimate
An estimated max is a guess about a lift you have not done. Your best set of five last month is a fact. Track the working sets and the trend across a training block tells you more than any single test ever will.
Common questions
How accurate is a one-rep max estimate?
Close enough to program with, and not close enough to bet on. Estimates are most reliable from sets of two to five reps. Past about eight reps the answer depends more on your pain tolerance and conditioning than on your maximum strength.
What is the difference between the Epley and Brzycki formulas?
Epley multiplies your weight by one plus reps divided by thirty. Brzycki divides by a term that shrinks as reps climb. They agree closely at low reps and diverge above ten, where Brzycki starts overestimating badly.
Which formula should I use?
Neither, exclusively. Use the average of the two as a planning number, then adjust it based on how the working sets actually feel.
Should I test my true one-rep max?
Rarely, if ever, unless you compete. A true maximum is fatiguing to recover from and gives you one data point. A set of five, logged every week, gives you fifty a year.
Does this work for every lift?
It works best on the big barbell lifts, where rep performance is limited by strength. It is much less reliable on isolation work and on anything where your grip or your balance fails before the muscle does.
Estimates guess. Your log knows.
Log every working set and watch your top set climb across months, not sessions. Free, no paid tier, and you can export the lot as CSV.