1RM Calculator (One-Rep Max)
Estimate your one-rep max (1RM) - the maximum weight you can lift for a single repetition - from a weight you can lift for multiple reps. The calculator uses the Epley and Brzycki equations and averages them.
How This Calculator Works
A true 1RM test (lifting the heaviest weight possible for one rep) is taxing and carries injury risk. Estimating it from a submaximal set is safer and practical for everyday programming. Two common formulas:
Epley: 1RM = weight x (1 + reps / 30)
Brzycki: 1RM = weight x 36 / (37 - reps)
This calculator reports the average of the two. For accuracy, use a weight you can lift for 1-10 reps - the further above 10 reps, the less reliable the estimate. Always perform the lift with strict form and a spotter or safety pins on heavy attempts.
References & Sources
Frequently Asked Questions
What is a one-rep max (1RM)?
Your 1RM is the most weight you can lift for exactly one repetition with proper form on a given exercise. It is the standard measure of absolute strength and is used to set training loads as a percentage of 1RM.
Which formula is more accurate?
The Brzycki formula tends to be more accurate for low rep ranges (1-5 reps), while Epley works reasonably across a wider range. This calculator averages both for a balanced estimate. For reps above 10, all formulas become less reliable.
Is estimating my 1RM safer than testing it?
Yes. A true 1RM test is physically demanding and risky, especially for beginners or without a spotter. Estimating from a weight you can lift for 5-8 reps gives a useful number for programming without the added risk of a maximal lift.
How do I use my 1RM for training?
Training loads are often prescribed as a percentage of 1RM: about 85-100% for strength (1-5 reps), 65-85% for hypertrophy (6-12 reps), and 50-65% for endurance (15+ reps). Use your estimated 1RM to set these loads and re-estimate every few weeks as you get stronger.
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