One-Rep Max Calculator
Estimate a one-repetition strength maximum using the Epley equation for a short set.
How the result changes
Only lifted load changes; all other inputs stay at your current values. The line illustrates the formula across the shown range. This is not a forecast of real-world outcomes.
About this calculation
One-Rep Max Calculator: Estimate a one-repetition strength maximum using the Epley equation for a short set. Enter lifted load, completed repetitions; the reported quantities are estimated one-rep maximum (kg), 80% training load (kg). The equations and examples below show how those inputs lead to the result and where the model's assumptions matter.
Formula
estimated 1RM = lifted load × (1 + repetitions / 30)
Worked example
With Lifted load: 80 kg, Completed repetitions: 5 reps, estimated one-rep maximum is 93.333333 kg.
Method and inputs
Use the heaviest clean set completed for one to ten repetitions. For more than one rep, multiply the load by one plus reps divided by thirty, the Epley estimate. A true single repetition is returned as the observed load rather than extrapolated.
Worked example
Lifting 80 kilograms for five reps gives 80 × (1 + 5/30), about 93.33 kilograms. Eighty percent of that estimated maximum is about 74.67 kilograms, a planning reference rather than a required workout weight.
The Epley estimate rises with reps for a fixed load: 80 kilograms for five reps predicts about 93.33 kilograms, while the same load for eight reps predicts about 101.33 kilograms. These estimates make sense only if both sets were near comparable effort.
How to read the result
The estimate predicts a potential one-rep performance; it is not a guarantee. Lift type, technique, fatigue and individual strength endurance affect the gap between predicted and observed maximum. It should guide training conservatively.
The eighty-percent output is an arithmetic training reference, not a complete program. Volume, fatigue, recovery and technique determine what load is appropriate on a particular day. A lifter returning from injury should use individualized guidance rather than chasing the estimate.
Assumptions and checks
The equation is most defensible for relatively low repetition counts, hence the ten-rep cap. Repetitions should be complete, consistent and close to a maximal effort. The model does not account for equipment assistance or spotting.
Do not enter body weight plus barbell weight unless that is the actual external load lifted for the exercise. Comparing Epley estimates from different exercises is not meaningful without context. Avoid attempting a maximal lift solely because an estimate suggests it.
Common questions
What does the one-rep max calculator calculate?
It estimates one-repetition maximum from a completed short set and displays an eighty-percent reference load.
When should I recalculate or check another method?
Recalculate after a comparable set or a direct tested maximum under safe supervision. If fatigue or technique changed, interpret movement in the estimate cautiously instead of treating every difference as a strength gain.
Inputs
- Lifted load (kg)
- Completed repetitions (reps)