One rep max calculator
Estimate your one-rep max from a set you’ve done, without testing a true max, and get training weights for every percentage.
Short answer
Estimated 1RM = weight × (1 + reps ÷ 30) (Epley). For example, 100 kg for 5 reps is about 115 kg. This calculator averages three formulas and gives a percentage chart for training.
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Formulas
Epley: weight × (1 + reps ÷ 30). Brzycki: weight × 36 ÷ (37 − reps). Lombardi: weight × reps0.1. We show the average. Estimates are best from sets of 3–6 reps close to failure and get less reliable above 10.
Strength on a cut
If your estimated 1RM holds or climbs while your weight drops, you’re almost certainly keeping your muscle. Log it next to your waist and photos every few weeks.
FAQ
Frequently asked questions
How accurate is a 1RM calculator?
Usually within about 5% for sets of up to 6 reps taken close to failure. Higher-rep sets and less experienced lifters see bigger errors.
Should I test my real one rep max?
You don’t need to. An estimate from a hard set of 3–5 is safer and good enough for planning training.
What percentage of 1RM builds muscle?
Anything from about 30% to 85% builds muscle if sets are taken close to failure; 65–85% (6–12 reps) is the most common range.