One-Rep Max Calculator

Calculate estimated 1RM for major lifts

About One-Rep Max Calculator

One-rep max (1RM) is the maximum weight you can lift for a single repetition of an exercise. Since testing a true 1RM is fatiguing and can be risky, this calculator estimates it from a lighter weight lifted for multiple reps, using the Epley formula.

Formula

1RM = Weight × (1 + Reps / 30)

How It Works

Enter the weight you lifted and the number of reps you completed with good form
The calculator applies the Epley formula to estimate your one-rep max
Results often also show percentages of your 1RM (e.g., 80%, 90%) useful for programming training weights

Tips

Estimates are most accurate for rep ranges of about 2-10 — very high rep sets (15+) produce less reliable 1RM estimates
Use estimated 1RM to program training percentages (e.g., 5 reps at 80% of 1RM) rather than testing a true max frequently
1RM estimates can vary between formulas (Epley, Brzycki, Lombardi) by a few pounds — treat the result as a close approximation, not an exact number

Frequently Asked Questions

How accurate is an estimated 1RM?

Estimated 1RM is typically within a few percent of your true one-rep max for moderate rep ranges (2-10 reps), though individual fatigue resistance and exercise type can shift accuracy.

What is the Epley formula?

1RM = Weight × (1 + Reps/30) — one of the most common formulas for estimating one-rep max from a submaximal set, developed by Boyd Epley.

Why not just test my actual one-rep max?

Testing a true 1RM requires maximal effort at high risk of injury and heavy fatigue, especially for beginners — an estimate from a lighter, higher-rep set is safer and still useful for programming.

How do I use my 1RM to plan training weights?

Multiply your 1RM by a target percentage — for example, 80% of a 200 lb 1RM is 160 lb, a common weight for sets of 5 reps in strength training.

Does the formula work the same for all exercises?

It's most reliable for compound barbell lifts (squat, bench press, deadlift); isolation exercises and bodyweight movements are less standardized and estimates can be less precise.