One Rep Max Calculator

Your one rep max (1RM) is the heaviest weight you can lift once with good form. You can estimate it from a lighter set instead of testing it. Lift 100 kg for 5 reps and your estimated 1RM is about 115 kg. This calculator averages four common formulas to get there.

Enter the weight you lifted in kilograms and the reps you completed, from 1 to 30. The tool shows the Epley, Brzycki, Lander and Lombardi estimates and their average. It then lists training loads from 95% down to 60% of that average, in 5% steps. If you enter 1 rep, the weight itself is treated as your 1RM.

The formulas agree closely at low reps and drift apart as reps rise. At 3 reps they sit within about 6 kg of each other. At 12 reps the gap grows to about 16 kg. Past about 10 reps, endurance plays a bigger part than strength, and estimates become less reliable. For the best estimate, use a hard set of 2 to 6 reps with clean form. The table below shows how the estimate changes with reps at 100 kg.

Percentages of 1RM are a common way to plan training. Heavy strength work often sits around 80% to 90% for low reps. Muscle-building sets often use about 65% to 80% for moderate reps. The right plan depends on your goals and experience. Estimating is safer than a true max attempt, especially for beginners. If you do test, warm up well, build up in small jumps and use a spotter or safety bars. Stop if anything hurts. The formulas work the same for pounds, as the units cancel out, even though the tool labels them kg. For cardio training, try the Heart Rate Zone Calculator.