What 1RM is used for
Your one-rep max is the heaviest weight you could lift once with full range of motion and acceptable form. Almost nobody needs to lift it regularly — but almost every serious program is written off it. Percentage-based training ("5×5 at 75%", "3×3 at 90%") is the standard language of strength programming because it scales the same plan to any lifter: 75% of a 200 kg squatter and 75% of a 100 kg squatter produce the same relative stimulus. Estimate your 1RM from an ordinary hard set, and the whole percentage system unlocks without ever maxing out.
The formulas — and when they disagree
This calculator shows two classic estimators. Epley (1985) is the headline number:
Brzycki (1993) is the common cross-check:
At 1 rep both return the weight itself, and up to about 5 reps they agree within a kilo or two. They drift apart as reps climb: at 100 kg × 8, Epley says 126.7 kg while Brzycki says 124.1 kg. That gap isn't a bug — it's an honest signal that high-rep sets measure endurance as much as strength. When the formulas disagree, the average is a sensible working number, and a lower-rep test set settles it.
The %1RM table explained
The table above converts your estimated max into training loads. Each percentage maps to a typical rep capacity — around 75% most lifters get ~10 reps, around 85% ~6 reps, around 95% ~2 reps — so a program calling for "4×6 at 80%" is asking for sets of 6 with roughly 2 reps in reserve. Loads are rounded down to the nearest 2.5 kg (or 5 lb), because "101.4 kg" doesn't exist on a barbell and rounding up turns prescribed reps into missed reps.
Rep capacity at a given percentage varies by person and by lift — squats usually allow more reps at a percentage than bench press. Treat the rep column as a starting map, then calibrate to your own logbook.
Testing a true max safely
If you do want a real bar-on-your-back number: earn it first. Test only lifts you've trained for months, on a fresh day, with safeties or a spotter set up. Work up in singles — roughly 50%, 70%, 80%, 90% of your estimate — resting 3–5 minutes between attempts, then make small jumps from 95%. Stop the session the moment form breaks down; a grindy 97.5% with good technique tells you more than an ugly PR. Beginners should skip all of this and program off estimates: the risk buys nothing a set of 5 can't tell you.
Programming with %1RM
The real power of a 1RM isn't the bragging number — it's that every set in a training block can be prescribed as a percentage and progressed deliberately: 70% week one, 75% week two, 80% week three, deload, retest. Doing that arithmetic by hand for one lifter is tedious; doing it for a full client roster is a spreadsheet job that eats coaching evenings. That's exactly what CoachRight's program builder automates — coaches prescribe sets as %1RM and the app computes each client's working weights, tracks every logged rep, and updates as they get stronger. If that's your Tuesday night spreadsheet, start a free 14-day trial. Training under a coach already? Your workouts, weights and PRs live in the free CoachRight client app.
Getting stronger also means eating for it — check the muscle gain calculator for your surplus and protein targets.