One-Rep Max (1RM) Calculator
Your one-rep max (1RM) is the most weight you can lift for a single repetition of an exercise. Rather than testing it directly, which is risky, this calculator estimates it from a lighter set: enter the weight you lifted and how many reps you managed, and it returns your predicted 1RM using the Epley, Brzycki and Lander formulas plus their average. Use it to set training loads as a percentage of your max.
Formula
Epley: 1RM = Weight × (1 + Reps/30); Brzycki: 1RM = Weight / (1.0278 − 0.0278 × Reps); Lander: 1RM = Weight / (1.013 − 0.0267 × Reps)
Example Calculation
Inputs
- Weight Lifted: 80 kg
- Repetitions: 8 reps
You lift 80 kg for 8 reps. The Epley formula gives 80 × (1 + 8/30) ≈ 101.3 kg, Brzycki gives 80 ÷ (1.0278 − 0.0278 × 8) ≈ 99.3 kg and Lander about 100.1 kg. Averaged, your estimated one-rep max is roughly 100 kg.
Frequently asked questions
What is a one-rep max?
It is the heaviest weight you can lift for one full repetition of an exercise with good form. It is the standard measure of maximal strength.
Why estimate instead of testing my 1RM directly?
Attempting a true max is tiring and carries a higher injury risk, especially without a spotter. Estimating from a submaximal set is safer and still accurate enough for programming.
Which formula should I trust?
All three are well established. Epley and Brzycki are the most common; the average of the three smooths out their differences and is a sensible number to train from.
How many reps give the best estimate?
Accuracy is highest at low reps. Sets of 10 reps or fewer give a reliable estimate; above about 12 reps the prediction drifts and overestimates.
How do I use my 1RM for training?
Set working loads as a percentage of it, for example 70-85% for strength. Recalculate every few weeks as you get stronger.