Free One Rep Max Calculator
Enter the weight you lifted and the reps you completed to estimate your one rep max, with a full percentage table for programming your training.
This free one rep max calculator estimates your 1RM from a submaximal set using the Epley, Brzycki, or Lombardi formula, then builds a percentage table (95% down to 50%) so you can pick training loads without maxing out.
Use a recent hard set, 1 to 12 reps, stopped 0 to 2 reps shy of failure.
Estimates for programming training, not medical advice. True max attempts carry injury risk; use a spotter and sensible progression.
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How 1RM estimation actually works
A one rep max is the heaviest weight you can lift once with good form. Testing it directly is fatiguing and risky, so lifters estimate it from a submaximal set: a weight they can lift for several reps. The formulas below translate reps at a given weight into a predicted max.
The Epley formula is the most common: 1RM = weight x (1 + reps / 30). Lift 225 for 5 reps and Epley predicts 225 x (1 + 5/30) = 262.5. The Brzycki formula, 1RM = weight x 36 / (37 - reps), gives a slightly more conservative 262.2 for the same set. Lombardi's version, weight x reps^0.1, lands nearby.
Accuracy falls as reps climb. Formulas are reliable in the 1 to 10 rep range and get shaky past 12, because endurance, not maximal strength, starts limiting the set. A 20-rep estimate is a guess dressed as math; test or use a lower-rep set instead.
The percentage table is where the estimate earns its keep. Most strength programs prescribe loads as percentages of 1RM: 85 to 95 percent for heavy strength work, 70 to 80 for hypertrophy volume, 50 to 65 for speed and technique work. Working from an estimated max keeps every session in the right zone without retesting.
One caution: the estimate assumes the set was near failure with good form. A casual set of 5 with 3 reps left in the tank will underpredict your max. For the best estimate, use a recent hard set where you stopped 0 to 2 reps shy of failure.
One rep max questions
What is a good one rep max formula?
The Epley formula, 1RM = weight x (1 + reps / 30), is the most widely used. Brzycki's formula gives a slightly more conservative estimate and many lifters prefer it for programming.
How accurate is a 1RM calculator?
Quite good for sets of 1 to 10 reps taken near failure, usually within 5 percent of a true tested max. Past 12 reps, endurance limits the set and estimates get unreliable.
Should I test my true one rep max?
Rarely. A true max attempt is fatiguing and carries injury risk. An estimate from a hard set of 3 to 8 reps programs training just as well for most lifters.
What percentage of 1RM builds strength?
Maximal strength work lives at 85 to 95 percent of 1RM, hypertrophy volume at 70 to 80 percent, and speed or technique work at 50 to 65 percent.