What is one rep max?
One repetition maximum, commonly written as 1RM, is the greatest load a person can lift once with valid technique for a specific exercise. It is specific to the movement, equipment, range of motion, and testing conditions.
An estimated 1RM uses a submaximal set instead of a direct maximal attempt. That makes it convenient for planning, but it remains a mathematical prediction.
Six 1RM prediction formulas
The calculator evaluates Epley, Brzycki, Lander, Mayhew, O'Connor, and Wathan. Selecting the average uses the arithmetic mean of all six estimates; selecting one formula makes that equation the primary result while still showing every comparison.
Brzycki: 100 × weight ÷ (102.78 − 2.78 × reps)
Lander: 100 × weight ÷ (101.3 − 2.67123 × reps)
Mayhew and Wathan use exponential equations, while O'Connor uses a linear multiplier. When the entered set is one repetition, every equation is set equal to the lifted weight.
Why the calculator shows a range
Different formulas can produce meaningfully different answers from the same set. The displayed range makes that uncertainty visible instead of implying that one exact prediction is guaranteed.
Lower-repetition sets generally transfer more directly to maximum-strength estimation. Research also shows prediction accuracy can differ across exercises and populations.
How to use the one rep max calculator
- Choose pounds or kilograms.
- Select an exercise label.
- Enter the weight and 1–15 completed repetitions.
- Select the six-formula average or a specific equation.
- Choose a practical plate-rounding increment.
- Select Calculate One Rep Max and review the range and loading table.
Using estimated 1RM in training
The percentage table converts the selected estimate into rounded loads from 50% to 100%. It does not prescribe sets, repetitions, frequency, or recovery. Those choices depend on experience, goals, technique, and program design.
Strength development also depends on adequate recovery and nutrition. The protein calculator can provide a separate daily nutrition estimate, while this page remains focused only on load prediction.
Limitations and lifting safety
A high-repetition set, inconsistent range of motion, poor technique, inaccurate plates, assisted repetitions, or stopping far from failure can distort the estimate. Machine and free-weight results are not interchangeable.
Do not attempt a calculated maximum solely because the tool displays it. Heavy lifting should use suitable equipment, warm-up, spotters or safety arms when appropriate, and qualified instruction.