Why estimate instead of testing
A true max attempt is the riskiest set in the gym and interferes with the training week around it. Rep-based estimation gets within a few percent for sets of 2–6 reps, costs nothing, and can be redone every session to track progress. Competitive lifters still test; everyone else mostly should not need to.
The four formulas
Epley and Brzycki are the two standards — they agree exactly at 10 reps and differ by only a couple of percent below that. Lombardi runs conservative at high reps; O'Conner sits between. We average all four for the headline number, which smooths out each formula's individual bias.
Using the percentage table
Programs prescribe loads as percentages of 1RM: strength work typically lives at 80–90% for 3–5 reps, hypertrophy at 65–80% for 6–12. The table converts your estimated max into those working weights directly — the highlighted row is the set you just entered, so you can sanity-check the estimate against how it actually felt.
Frequently asked questions
Which formula should I trust?
For sets of 2–6 reps they barely disagree, so the average shown is fine. Brzycki tends to be slightly conservative at higher reps, Epley slightly generous — if you must pick one, pick whichever matches your tested max best and stay with it.
Does this work for every exercise?
The formulas were validated mostly on barbell lifts — squat, bench, deadlift. They are rougher for isolation movements and machines, and rep-max testing matters less there anyway.
Is this medical advice?
No. The Epley and Brzycki formulas, which agree closely at low reps and diverge above about ten. Testing a true one-rep max is where lifters get injured; the estimate exists so you do not have to.
Is my data stored or sent anywhere?
No. Your lifting numbers stay on your machine.
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