1RM Calculator

Maximum strength without a maximum attempt

Your one rep max is the weight you can lift exactly once with good form. Testing it directly is demanding and not without risk.

The calculator estimates it instead: enter a weight and the number of reps you managed with it, and it derives the theoretical maximum.

How it is calculated

Epley: 1RM = weight × (1 + reps / 30). Brzycki: 1RM = weight / (1.0278 − 0.0278 × reps). Lander: 1RM = weight / (1.013 − 0.0267123 × reps). The calculator shows all three and their average.

The three formulas are regressions from strength tests; they agree well up to about 10 reps and drift apart beyond that — hence the cap at 20 reps.

Example: 80 kg for 5 reps. Epley = 80 × (1 + 5 / 30) = 80 × 1.167 = 93.3 kg. Brzycki = 80 / (1.0278 − 0.139) = 80 / 0.889 = 90.0 kg. Lander = 80 / (1.013 − 0.134) = 80 / 0.879 = 91.0 kg. Average = 91.4 kg.

Training weights come from the 1RM as percentages, rounded to 0.25 kg because that is the smallest plate.

To calculate your 1RM, use a set taken close to failure with 3 to 8 reps — that is where the estimate is most accurate.

What you need it for

Training plans often give weights as a percentage of your maximum. Without that number you cannot apply them.

The estimate is most accurate at three to eight reps. Twenty reps measures endurance more than strength.

Frequently asked questions

How accurate is the estimate?

Quite accurate at low rep counts, less so as reps rise. Different formulas give slightly different values.

Do endurance athletes need this at all?

As a way to steer strength work, yes. In endurance sport it is less about maximum strength than stability and injury prevention.

Should I test my true maximum?

Only with experience, good technique and a spotter. For most people the estimate is entirely sufficient.