One Rep Max Calculator
Estimate one-repetition maximum strength from a lifted weight and repetition count using Epley, Brzycki and Lombardi formulas.
Enter your values
Change any assumption and calculate again to compare results.
What a one-rep max estimate tells you
A one-repetition maximum, or 1RM, is the heaviest load a person can lift once with proper technique. Testing a true maximum is not always practical, so formulas estimate 1RM from a submaximal set.
This calculator uses three common equations. Epley increases the lifted weight by a factor based on reps, Brzycki uses a ratio that rises as repetitions increase, and Lombardi uses a power relationship. The result displays each estimate and their average.
Use moderate-rep sets for better estimates
Most 1RM equations are most useful when the set is relatively close to maximal effort and the repetition count is not very high. As reps rise, fatigue, exercise selection and individual endurance can create larger differences between formula estimates.
For practical training, a set of roughly 2–10 hard repetitions often gives a more useful estimate than a very high-repetition set. The calculator accepts up to 20 reps but displays the formula spread so you can see uncertainty.
Training safety
An estimated 1RM is not a requirement to attempt that load. Technique, spotting, equipment, injury history and training experience matter.
Use conservative loads when learning a movement and follow qualified coaching or clinical advice when returning from injury.
Important information
This calculator is for general education and planning. It is not a diagnosis, medical device or substitute for individualized healthcare advice. Measurements and formula estimates can differ from clinical assessments.
If the result could affect treatment, pregnancy care, medication, driving, military status or another safety-sensitive decision, confirm it with the appropriate qualified professional or official process.
Frequently Asked Questions
What happens if I enter 1 repetition?
The calculator returns the lifted weight itself as the 1RM estimate.
Why do the formulas give different answers?
Each equation models the relationship between reps and maximum strength differently, so variation is expected.
Can I use pounds or kilograms?
Yes. The formula works with either unit as long as the same unit is used for input and result.