Your 1RM is the foundation of strength programming. Here's how to estimate it safely from sub-maximal lifts, which formula is most accurate, and how to use it to set training weights.
Trying to find your true one-rep max in the gym is risky and unnecessary. With a simple formula, you can estimate it accurately from a set you can do safely — and that estimate is often more useful for programming anyway.
The Epley formula is the most commonly used and is accurate for most people in the 1–10 rep range. It starts to overestimate as reps increase — don't use it for sets of 15 or more.
All formulas become less accurate above 10 reps. For the most reliable estimate, test with a weight you can do for 3–5 clean reps with good form.
Once you have your estimated 1RM, you can calculate working weights for any rep range:
Example: 1RM squat estimated at 120kg. For a hypertrophy session at 70%: 120 × 0.70 = 84kg for sets of 8–12 reps.
The formula is an estimate, not gospel. Individual variation in fibre type composition means some people are "1-rep specialists" (more fast-twitch muscle, neurally efficient) and others are "high-rep specialists." The formulas tend to underestimate the 1RM of high-rep specialists and overestimate for low-rep specialists.
Never use the estimated 1RM to attempt an actual 1RM without proper warm-up and preparation. If the formula says your bench press 1RM is 110kg but you've never lifted over 90kg, don't load 110kg onto the bar. Build up gradually over multiple sessions.
Retest regularly. 1RM estimates go stale as you get stronger. Recalculate every 4–8 weeks to ensure your training percentages stay meaningful.