How 1RM is estimated
Both formulas estimate the heaviest weight you could lift for a single rep, based on a lighter weight lifted for multiple reps. They tend to diverge more as rep count increases.
- weight — the weight lifted, in kg
- reps — reps completed with that weight
More detail
Epley (1985) vs. Brzycki (1993)
Epley's formula is linear and stays closer to the true max at higher rep counts. Brzycki's formula assumes a roughly linear drop in strength per rep and is often considered more accurate in the 2–10 rep range, but becomes unstable as reps approach 37, where its denominator hits zero.
Tip. Estimates are most reliable using a set of 2–8 reps taken close to failure. For anything above 10–12 reps, treat the number as a rough ballpark rather than a training target.
Frequently asked questions
Epley vs. Brzycki — which is more accurate?
Brzycki tends to be more accurate in the 2–10 rep range but becomes unstable near 37 reps, where its denominator hits zero. Epley stays linear and holds up better at higher rep counts. Check both above — they usually land within a few kg of each other for typical sets.
How many reps should I use for an accurate estimate?
2–8 reps taken close to failure gives the most reliable estimate. Enter your weight and rep count above — sets beyond 10–12 reps drift further from your true 1RM and should be treated as a rough ballpark.
Why do the two formulas give different numbers?
Epley assumes a constant percentage drop per rep; Brzycki assumes a roughly linear drop in strength per rep. They diverge more as your rep count increases, which is why both are shown above.
Is my estimated 1RM safe to actually attempt?
Not directly — it's a statistical projection from submaximal reps, not a tested max. If you want your true 1RM, work up to it gradually with a spotter or safety bars rather than jumping straight to the estimated number.