One-Rep Max Calculator
Your one-rep max (1RM) is the heaviest single clean rep you can lift. Estimate it from a hard working set — no risky max-out needed — and get the percentage chart most programs are built on.
How to use this calculator
- Work up to a challenging set of 1–12 reps with clean form on the lift you want to test.
- Enter the weight you lifted and how many reps you completed.
- Compare the five formula estimates and use the load chart to plan working weights.
How 1RM formulas work
All rep-max equations extrapolate from submaximal performance. The two most cited:
Epley (1985): 1RM = w × (1 + reps ÷ 30)Brzycki (1993): 1RM = w × 36 ÷ (37 − reps)We also show Lombardi, O'Conner and Mayhew estimates. Expect the formulas to agree within a few percent for sets of 3–8 reps and to spread wider above 10. For most people, Epley sits mid-pack, which is why it is our headline number.
Using the percentage chart
Strength programs prescribe intensity as a percentage of your 1RM — for example 5×5 at 80%, or speed work at 65–70%. The chart in your result converts each percentage band back to actual weights, with the rep count you can typically expect at that load.
Frequently asked questions
Which formula should I trust?
For sets of 3–8 reps they all land close together. Average a few, or just use Epley — its mid-range behavior suits most lifters. Re-estimate every 4–8 weeks as you progress.
Why do the formulas give different answers?
Each was derived from a different population and rep range. Reps-to-fatigue curves differ by lift, speed and training age, especially above 10 reps.
How accurate is an estimated 1RM?
Within roughly 5–10% for sets under 10 reps. Higher-rep sets inflate estimates because muscular endurance, not maximal strength, becomes the limiter.
How do I use percentages in my program?
Multiply your 1RM by the prescribed percentage (the chart does it for you). Most hypertrophy work lives at 65–80%, strength blocks at 80–95%.