One Rep Max Calculator
Your one rep max, estimated from sets you already did — no max attempt, no spotter, no bad week.
The formula
Gym Journal uses the Epley formula: 1RM = weight × (1 + reps ÷ 30).
So a set of 100 kg for 5 reps estimates to 100 × (1 + 5 ÷ 30) ≈ 117 kg. A set of 100 kg for 8 estimates to about 127 kg.
Every estimator drifts as the rep count climbs, because a set of fifteen is testing something closer to endurance than to maximal strength. Estimates from sets in roughly the 1–10 range are the ones worth reading.
Why estimate instead of test
Testing a true one rep max is expensive: it needs a spotter, it needs a good day, and it costs you recovery you could have spent training. Estimating from your best set of the day costs nothing and can be done every session.
Because it updates continuously, the estimate is most useful as a trend rather than a number. A line that climbs over months is the signal; any single day’s value is noise.
Where to find it
Gym Journal computes the estimate from your best set each day and charts it per exercise, alongside volume load and a consistency heat map. You do not enter anything extra — logging the set is what produces the number.
It’s free, and it’s in the app
439 exercises, 40+ ready-made routines, and unlimited workout logging — no account required to start.
Frequently asked questions
Which 1RM formula does Gym Journal use?
The Epley formula: 1RM = weight × (1 + reps ÷ 30). It is calculated from your best set on each day you trained that exercise.
How accurate is an estimated 1RM?
It is an estimate, and it is most reliable from sets in the 1–10 rep range. Read it as a trend line over weeks rather than as a number to attempt on the day.
Do I need to test my max to use it?
No. That is the point of estimating — logging your normal working sets is enough to produce and track the number.