Complete guide
One rep max calculator using four 1RM equations
Enter a completed training weight and one to 15 repetitions. Calculator24 calculates four equation estimates, reports their average and creates practical percentage loads from 50% through 100%.
What an estimated 1RM means
A one-repetition maximum is the greatest load completed once with acceptable technique. Prediction equations estimate it from a lighter set so a direct maximal attempt is not required.
Four equations used
The calculator displays every estimate before averaging them. Seeing the spread is more transparent than presenting one formula as exact.
Epley=w×(1+r/30)Brzycki=w×36/(37−r)Lander=100w/(101.3−2.67123r)Mayhew=100w/(52.2+41.9e^(−0.055r))Worked five-repetition example
For 100 units completed five times, the equations use the same observed set but different fatigue curves. The result table shows the numerical spread and mean.
Why estimates differ
Research finds equation performance can vary by exercise, sex, training status, age and repetition range. A bench-press equation result may not transfer perfectly to a squat or machine exercise.
Choosing a repetition count
Lower-repetition sets are generally closer to the target maximum. This tool caps input at 15 repetitions because extrapolation becomes less dependable as the test moves farther from a true maximum.
Using the training table
Percentage loads are planning references. Round for available plates and reduce the load when technique, pain, fatigue or coaching guidance calls for it.
Displayed prediction equations
| Equation | Expression |
|---|---|
| Epley | w × (1 + r/30) |
| Brzycki | w × 36/(37 − r) |
| Lander | 100w/(101.3 − 2.67123r) |
| Mayhew | 100w/(52.2 + 41.9e^(−0.055r)) |
Frequently asked questions
Is an estimated 1RM exact?
No. It is an equation-based estimate from one observed set.
Which equation is best?
Performance depends on the exercise and population, so the tool shows four.
Can I enter kilograms?
Yes. Equations preserve the selected weight unit.
Why stop at 15 reps?
Higher repetitions require a larger extrapolation and can reduce precision.
Should I attempt the displayed maximum?
Only when appropriate for your experience, technique, health and supervision.
Why does one repetition equal the lifted weight?
A completed one-repetition set is already the observed 1RM for that set.
What to keep in mind
An estimated 1RM is not a guarantee of a safe maximal lift. Technique, exercise, fatigue, training history, supervision and the population behind each equation affect accuracy.
Results display up to 8 decimal places; exported numbers preserve calculation precision. This is a calculation summary, not an official certificate.