Fitness & Sports
One-Rep Max Calculator
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How to use it
Using the one-rep max calculator
- 01
Log a hard set
Use a weight you could lift between 1 and 12 times; 3 to 8 reps gives the most reliable extrapolation.
- 02
Enter weight and reps
Kilograms and whole repetitions; anything above 12 gets rejected as statistically unreliable.
- 03
Program from percentages
Strength blocks typically train at 80–90% of this number; the 90% row is pre-computed.
Good to know
Why not just test your true max?
Genuine one-rep attempts demand maximal neural readiness, ideal technique and a spotter; and they cost recovery. Submaximal testing every few weeks plus these formulas tracks progress with a fraction of the injury risk.
Choosing between the formulas
Under six reps they differ by under two percent; many coaches simply take whichever estimate is lower for programming conservatism. The divergence beyond ten reps is exactly why input stops at twelve.
Common percentage schemes
- 5×5 strength: ~80–85% of estimated 1RM.
- Hypertrophy: 65–75% for 8–12 reps.
- Speed/power work: 50–60%, moved fast.
How it's calculated
The math behind this calculator
Epley: 1RM = w × (1 + reps ÷ 30)
Brzycki: 1RM = w × 36 ÷ (37 − reps)Both formulas extrapolate a submaximal set up to a theoretical single repetition. Epley’s linear model is the strength-training default; Brzycki’s hyperbolic version tracks it closely at low rep counts and diverges slightly toward twelve.
We cap input at 12 reps because beyond that the estimates balloon while real maximal-effort predictions collapse; fatigue and fiber-type differences dominate the math.
Assumptions & limitations
- Set taken close to technical failure.
- Compound lifts (squat, bench, deadlift) fit the models best.
- Estimates; actual maxes vary by several percent with warm-up, sleep and adrenaline.
Worked example
Five clean reps at 100 kg project to roughly a 116.67 kg one-rep max by Epley, with Brzycki agreeing near 112.5 kg; program percentages off the lower figure if unsure.
FAQ
Frequently asked questions
- Which formula should I use?
- Epley for general use; it is the de facto standard. Check Brzycki when rep counts climb past eight; if they diverge much, your set was probably not near failure.
- Does it work for isolation machines?
- Loosely. Machine leverage varies wildly by brand, so treat those numbers as machine-specific personal benchmarks only.
- Why reject more than 12 reps?
- Extrapolation error grows nonlinearly with rep count; beyond a dozen the formulas routinely overpredict by 10%+ versus tested maxes.
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