One-Rep Max Calculator (1RM)

Testing a true max is the riskiest set in a training block, and most people do not need to. A hard set of three to six reps already says roughly what one rep would be. This calculator turns that set into an estimated one-rep max, then into the weights to load for the percentages your program asks for.

Rather than trusting one equation, it runs seven published ones and shows them side by side, so you can see how much they agree. The figure at the top is their average, with the range underneath and the same number converted between kilograms and pounds.

Worked Example: 100 kg for Five Reps

The page opens on a set of 100 kg for 5 reps. The estimate comes out at 115.5 kg, with the formulas spread from 112.5 kg (Brzycki and O'Conner) to 119.0 kg (Mayhew). At 80% the training table loads 92.5 kg for about 8 reps, rounded to the nearest 2.5 kg. Change Round to to 1.25 kg if you own fractional plates, or switch to pounds, where the step moves to 5 lb.

Enter a single rep and the formulas step aside: one rep is the max by definition, so 315 lb for 1 returns 315 lb.

The Seven Formulas Behind the Estimate

• Epley: weight × (1 + reps ÷ 30).
• Brzycki: weight × 36 ÷ (37 − reps).
• Lander: 100 × weight ÷ (101.3 − 2.67123 × reps).
• Lombardi: weight × reps^0.10.
• Mayhew: 100 × weight ÷ (52.2 + 41.9 × e^{−0.055 × reps}).
• O'Conner: weight × (1 + 0.025 × reps).
• Wathan: 100 × weight ÷ (48.8 + 53.8 × e^{−0.075 × reps}).

The About column in the training table reverses Epley to estimate how many reps each percentage allows. Below 60% that count passes 20 and is shown as “20+ reps”, since the number stops meaning much at that point.

Accuracy Past Ten Reps

All seven equations were fitted to sets in the low to moderate rep range, and they drift apart as reps climb. For 60 kg × 10 they range from 75.0 to 80.8 kg, and the page shows a warning once you enter more than 10 reps. Reps above 20 are refused with“Reps must be a whole number from 1 to 20.”, and loads are capped at 1,000 kg or 2,205 lb.

An estimate also assumes the set was close to failure with good form. A set stopped well short of failure gives a low estimate, and the result will always run a little different between a squat, a bench press and a deadlift. Use it to set training loads, not to replace a supervised max attempt.