Four formulas, one honest range
Your one-rep max is the most you could lift for a single rep — but you don’t have to actually attempt a max to estimate it. From a set you’ve already done (a weight and the reps you hit), several published formulas can predict it. The catch: they don’t agree. So rather than pick one, this calculator runs Epley, Brzycki, Lombardi and Lander and shows you the spread, marks the median and flags the formula closest to it.
The four formulas
- Epley (1985) — the most widely used; linear in reps.
- Brzycki (1993) — popular in strength circles; slightly lower at high reps.
- Lombardi (1989) — a power-curve model.
- Lander (1985) — close to Epley across common rep ranges.
All four are established, peer-referenced prediction equations. The fewer reps your set was (ideally 1–10), the tighter and more reliable the estimate.
FAQ
How accurate is a 1RM calculator?
Most accurate when your set was 1–10 reps. Beyond that, all formulas lose precision and the estimates spread out — which is why seeing the range matters more than a single number.
Which 1RM formula is best?
None is universally “best” — they were fitted to different data. Epley is the most common; Brzycki tends lower at high reps. Showing all four is more honest than defending one.
Do I need to attempt a true max?
No — that’s the point. You estimate your max from a submaximal set you’ve already done, which is safer than a genuine max attempt.
Can I work out my training weights from this?
Yes — from an estimated 1RM you can back out percentages for different rep targets. The training-load table on this page does exactly that.