One Rep Max Calculator (1RM)

A one rep max (1RM) calculator estimates the heaviest weight you could lift for a single repetition, from a weight you can lift for several reps. Enter the weight and the number of clean reps you did to (or close to) failure. You get your estimated 1RM and a table of training weights, with no need to test a true max.

One rep max calculator

This calculator needs JavaScript. The formulas are explained below.

What is a one rep max?

Your one rep max (1RM) is the maximum weight you can lift for one full repetition of an exercise with good form. A 1RM calculator estimates it from the weight you work with and the number of reps you can do with that weight.

Why it helps to know your 1RM

Knowing your estimated 1RM helps you in a few ways:

• Setting goals: you have a clear number to beat.
• Measuring progress: if your estimated 1RM goes up over the weeks, you are getting stronger, even when your working weights and reps change.
• Planning your training: many programs give weights as a percentage of your 1RM. The table under the calculator does that math for you.
• Choosing weights safely: you can pick working weights that fit your strength without testing a true max, which is hard and needs experience, a warm-up and a spotter.

If you do want to test your real 1RM, the calculator helps you prepare: it tells you roughly where to aim, so you can plan your warm-up sets.

The calculator works best for multi-joint strength exercises such as the squat, the deadlift, the Romanian deadlift, the bench press and the shoulder press.

The formula behind the calculator

The calculator uses the Epley formula, one of the most popular formulas in fitness. It is named after Boyd Epley, a strength and conditioning coach at the University of Nebraska, who published it in 1985. It estimates the most you can lift for one rep based on the weight you lift for a certain number of reps:

• 1RM = W × (1 + R / 30)
• W: the weight you lift in the exercise
• R: the number of reps you do with that weight

The formula is built on the idea that there is a steady relationship between the weight you lift, the number of reps you can do with it, and your one-rep maximum. For comparison, the calculator also shows the Brzycki formula, another common one: 1RM = W × 36 / (37 − R). The two give almost the same result at around 10 reps and differ a little at lower reps.

How accurate is the estimate?

There are many formulas and methods for estimating 1RM. The Epley formula gives a reasonable estimate for most people, but it is not perfect, and the result can be off. Your technique, genetics, strength level, body structure and the exercise itself all affect it.

The estimate is more accurate when you use fewer reps. In a study of 70 men and women on the bench press and the leg press, of 5-, 10- and 20-rep tests, the 5-rep tests predicted the 1RM best, and the authors advised using no more than 10 reps in these estimates. That is why the calculator accepts 1 to 12 reps and warns you above 10.

For the best estimate:

• Use a set of about 3 to 10 reps.
• Count only reps with full range of motion and good form.
• Use a set taken to failure or one rep short of it.
• Compare results for the same exercise over time, not between exercises.

Using the percentage table

The table under the result shows weights at 60% to 95% of your estimated 1RM, with the approximate number of reps each weight allows by the Epley formula. For example, heavy strength work often uses about 80-90% of 1RM for 3 to 6 reps, and muscle-building work often uses about 60-80% for 6 to 15 reps. Treat the rep numbers as a guide: in real training, most people can do more reps than the formula predicts on some exercises and fewer on others.

How to test a real 1RM safely

If you are experienced and want to test your true max:

• Warm up well, then do a few sets of low reps, building up gradually.
• Use a spotter for the bench press, and safety bars in a squat rack.
• Rest 3 to 5 minutes between heavy attempts.
• Stop the test when your form breaks down. A failed rep with bad form is not worth it.

If you are a beginner, you don't need a true max test. The calculator gives you enough to plan your training.

Bottom line

A one rep max calculator turns the sets you already do into a strength number you can track. Use a set of 3 to 10 good reps, write the result down, and check it again every few weeks. When it goes up, your training is working.

Frequently asked questions

How many reps should I use for the calculator?

A set of about 3 to 10 reps gives the best estimate. Above 10 reps, the estimate gets less reliable.

Is the Epley or the Brzycki formula better?

Neither is best for everyone. They give similar results, especially around 10 reps. Pick one and use it every time, so your numbers stay comparable.

Can I use the calculator for any exercise?

It works best for multi-joint exercises like the squat, deadlift, bench press and shoulder press. For small isolation exercises, such as curls or lateral raises, a 1RM is less useful.

Does the calculator work in pounds?

Yes. Enter the weight in pounds or kilograms; the result is in the same unit.