One-Rep Max Calculator

What this generator does

Applies both the Epley and Brzycki formulas to the weight and reps you enter, compares them, and builds a table of training weights for common rep counts. Each estimate is then solved back for the reps it came from.

How to use this tool

1. Enter the weight and how many good reps you managed.
2. Read both estimates and the gap between them.
3. Use the table to find weights for other rep counts.
4. Note that these are estimates, not permission to attempt the lift.

Understanding the controls

Weight lifted

In whatever unit you train in — the estimate comes back in the same one.

Reps completed

How many good repetitions. Both formulas lose accuracy above about ten reps, and Brzycki breaks down entirely as it approaches its limit.

Common use cases

• Estimating a one-rep max without attempting one
• Setting training weights as percentages of an estimated max
• Comparing two standard formulas on the same set
• Converting a five-rep set into a three-rep target
• Tracking an estimated max across a training block

How this generator works

Epley multiplies the weight by one plus the reps over thirty; Brzycki divides by a term that falls as the reps rise. Both are curves fitted to observed data rather than derived from anything, which is why they diverge. Before display each estimate is recomputed, each is solved back for the reps it came from and must return them, a single rep is confirmed to estimate the weight itself under Brzycki, and the training table is confirmed to give lighter weights for more reps.

Randomness and fairness

Nothing here is random. A weight and a rep count give exactly two estimates. Nothing here is medical or coaching advice; these are arithmetic models, and how you train is a matter for you and anyone qualified you ask.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

• These are estimates from population data, and individuals vary a great deal — someone with high endurance will beat their estimate at high reps and miss it at one.
• Accuracy falls sharply above about ten reps, where the formulas diverge most.
• The estimate assumes the set was taken close to failure with good form; a comfortable set will underestimate.
• An estimated maximum is not a lift you have done, and attempting a true maximum is not something a calculator should encourage.Nothing here is medical or coaching advice; these are arithmetic models, and how you train is a matter for you and anyone qualified you ask.

Privacy and your data

The estimates are computed in your browser. The weight and reps you enter are never transmitted, stored or included in analytics.