One-Rep Max Calculator
Take a set you have already finished and work out the single heaviest rep you could probably do. Useful for setting training percentages without ever having to test a true max.
Enter the weight you lifted and how many reps you got.
Four estimators, and why you get all four.
Epley, Brzycki, Lombardi and O'Conner each fit a curve to how many reps people manage at a given fraction of their max. They agree closely at low reps and drift apart above about eight, so showing one number would hide how much of it is guesswork. The headline figure is the average of the four; the spread underneath is the honest error bar.
Accuracy depends entirely on the set being taken close to failure. A set of eight with three left in the tank tells the formula almost nothing. Sets of one to five give the tightest estimates, which is why this calculator stops accepting reps above 12.
With bands, treat this as directional. A band gets heavier as it stretches, so the resistance at your sticking point is not the resistance at lockout, and none of these formulas were fitted on an ascending strength curve. Use it to compare a set against your own previous sets, not to compare a band lift against a barbell lift.
Numbers are the easy part.
Rubber Bands turns a goal into a schedule you can actually keep, built around the resistance bands you already own.