One-Rep Max Calculator

Your one-rep max (1RM) is the heaviest weight you can lift once with good form. Testing it directly is tiring and carries some risk, so most lifters estimate it from a set of several reps. Enter the weight and the number of reps you completed, and this calculator gives estimates from five published formulas, their average, and a table of loads for different rep targets that you can use to plan training.

It works for any barbell or machine lift, such as the squat, bench press and deadlift, in kilograms or pounds.

Epley: 1RM = w × (1 + r ÷ 30)

Brzycki: 1RM = w × 36 ÷ (37 − r)

Mayhew: 1RM = 100 × w ÷ (52.2 + 41.9 × e^(−0.055 r))

w is the weight lifted and r the reps completed. Lombardi uses w × r^0.10, and Wathan has the same exponential form as Mayhew with different constants. Epley and Brzycki give nearly identical results at around 10 reps but differ at low and high rep counts, which is why the average is a reasonable single figure.

100 kg for 5 reps. Epley gives 116.7 kg and Brzycki 112.5 kg; the average of all five is 116.4 kg. For sets of 8, use about 93.2 kg (80%).

225 lb for 8 reps. Epley gives 225 × (1 + 8/30) = 285 lb, and the average is about 283 lb.

Prediction formulas are most accurate with sets of 3 to 6 reps taken close to failure. With 10 or more reps, muscular endurance plays a bigger role and errors grow, often overestimating the max for some lifts and underestimating it for others. Use a set done fresh, after a warm-up, with consistent depth and range of motion. Estimates from machine exercises and smaller muscle groups are less reliable than from the main barbell lifts.

Many lifters now judge effort by reps in reserve (RIR), how many more reps they could have done, or by a rating of perceived exertion (RPE) on a 10-point scale where 10 means no reps left. If you stop a set with two reps in reserve, add those to the reps you did before using the calculator: 100 kg for 5 reps at RPE 8 is roughly a 7-rep max, which gives a higher and more accurate estimate. Being honest about effort matters more than the choice of formula.

Before a heavy set or a max attempt, start with the empty bar or a light load for 8 to 10 reps, then make three or four jumps of decreasing reps, for example 50% for 5, 70% for 3, 80% for 2 and 90% for 1, resting a few minutes between the heaviest sets.

Strength programs prescribe loads as percentages of 1RM. Heavy sets of 1 to 5 reps at 85% or more build maximal strength; sets of 6 to 12 at roughly 65 to 85% are typical for muscle growth; and lighter sets of 12 to 20 develop muscular endurance. Recent research shows that muscle growth is similar across a wide range of loads as long as sets are taken close to failure. Re-estimate your max every four to eight weeks as you get stronger, and use a spotter or safety bars for heavy sets.