One-Rep Max Calculator

What is a one-rep max?

Your one-rep max (1RM) is the heaviest weight you can lift for a single clean repetition of an exercise. Testing it directly is risky, so this calculator estimates it from a set you've already done — for example, 5 reps at 100 lb — using two well-established formulas and averaging them.

Epley and Brzycki

Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps). They agree closely at low reps and drift apart as reps climb, which is why estimates are most reliable at 10 reps or fewer.

Using the percentage table

The table shows common training loads as a percentage of your 1RM — useful for programming. Strength work often lives at 85–95%, hypertrophy around 67–80%, and endurance below 67%.

FAQ

Should I actually lift my estimated max?

Only with a spotter, proper warm-up, and good form — and never on isolation movements. The estimate is mainly a programming tool, not a cue to test a true max every week.

Is this 1RM calculator free to use?

Yes, it's completely free with no sign-up, and you can estimate your max for as many lifts as you want.

Is my data private?

Yes. The weight and reps you enter are calculated in your browser and never sent to a server, so your training numbers stay on your device.

How many reps should I use for an accurate estimate?

Use a set of about 10 reps or fewer for the most reliable result. The Epley and Brzycki formulas were validated in the low-rep range, and their accuracy drops as reps climb because muscular endurance starts to outweigh pure strength.

Does it work for any lift?

The estimate works best for compound barbell lifts like the squat, bench press, and deadlift, where high-rep sets to near failure are practical and safe-ish. It's far less reliable for isolation movements such as curls, where small form changes swing the numbers.

Does it work on mobile?

Yes. The calculator and percentage table are responsive, so you can check your training loads on a phone right in the gym.