How to estimate your one-rep max
Your one-rep max (1RM) is the most weight you can lift for a single rep. Testing it directly is risky and fatiguing, so most lifters estimate it from a set they've already done — say, 100 kg for 5 reps. The more reps in the set, the less accurate any estimate becomes, so a top set of 1–5 reps gives the most reliable number.
Why six formulas instead of one
There's no single "correct" 1RM formula — Epley, Brzycki, Lombardi, O'Conner, Mayhew and Lander each model the rep-to-weight curve slightly differently, and they disagree by a few percent. Most calculators pick one and hide the uncertainty. This one runs all six and shows you the average plus the spread, so you can see how confident the estimate actually is. A tight spread means the formulas agree; a wide one (usually from high-rep sets) means treat the number with caution.
The rep-max table
Once your 1RM is estimated, the table works backwards to show what you should be able to lift for any number of reps — your 3-rep max, 5-rep max, 8-rep max and so on — as both a weight and a percentage of your 1RM. It's the fastest way to pick working weights for a program, and each row is rounded to real plate math so you can load the bar without doing arithmetic between sets.
A note on accuracy
Estimates are exactly that. Your true max depends on your training, technique, leverages and how the lift fatigues you — a deadlift 1RM estimated from 10 reps will read high because deadlifts hold up poorly at high reps. Use the number as a planning tool and a progress marker, not gospel, and never chase an estimated max on a bad day.