What is a one rep max (1RM)?
Your 1RM is the heaviest weight you can lift once with good form in a given exercise, such as the bench press, squat or deadlift. Coaches use it to set training weights as a percentage of it instead of guessing. Rather than testing a true max (which carries injury risk), the calculator estimates it from a normal set taken to failure.
How we calculate it
- Epley: weight × (1 + reps ÷ 30).
- Brzycki: weight × 36 ÷ (37 − reps).
- The main result is the average of both, because the two formulas differ by a few percent (Epley is a little higher below 10 reps, Brzycki above).
Example: 100 kg for 5 reps → Epley = 116.7, Brzycki = 112.5, average about 114.6 kg.
How to use the percentages
Based on National Strength and Conditioning Association (NSCA) guidelines:
- Strength: 85% of 1RM or more, for 6 reps or fewer.
- Hypertrophy (muscle growth): 67–85%, for 6–12 reps.
- Muscular endurance: below 67%, for 12 reps or more.
Frequently Asked Questions
Why only up to 12 reps?
The formulas are most accurate at low reps. With high reps, the difference between people grows a lot (muscle fibre type, endurance). For the best estimate, use a set of 3 to 8 reps.
Should I calculate it for each exercise?
Yes. Your 1RM is different for each lift, so use a set from the same exercise: bench press, squat and deadlift each get their own number.
Do I need to test my true max?
No, and it isn’t recommended for beginners. The estimate is enough to set your training weights. If you do test it, warm up thoroughly and use a spotter.
My real max differs from the estimate. Which is right?
What you actually lifted is right. The formulas are averages and can be off by 5% or more depending on the person and the lift. Use the calculator as a starting point and adjust to your performance.
How many calories did my workout burn?
Try our calories burned calculator, and for your protein needs while building muscle, our protein and macro calculator.