One-Rep-Max Calculator
Enter a weight you lifted and the number of clean reps you completed to estimate your one-rep max (1RM) — the most you could lift for a single rep — using three published strength-science formulas.
Estimated one-rep max
Your training weights
| % of 1RM | ≈ reps | Weight |
|---|
How it works
A one-rep max (1RM) is the heaviest weight you can lift for a single repetition. Because testing a true 1RM is fatiguing and carries injury risk, strength coaches usually estimate it from a lighter set taken close to failure. This calculator averages three published formulas:
- Epley: 1RM = weight × (1 + reps / 30)
- Brzycki: 1RM = weight × 36 / (37 − reps)
- Lombardi: 1RM = weight × reps0.10
The three agree closely at low reps and diverge as reps climb — which is why the estimate is most reliable from sets of about 2–10 reps. Above ~10 reps, individual endurance differences make any 1RM estimate much rougher.
Using the percentage table
Once you have an estimated 1RM, the %1RM → reps table gives a standard guideline for how much to load for a given rep target — for example, ~80% of 1RM for sets of 8. These are widely-published training guidelines (NSCA), not rules: your own rep capacity at a given percentage varies with the exercise, your training history, and the day.
Putting the number to work
Use the estimate to program load — not to chase a max every session.
- Estimate from a set of 3–8 clean reps for the most reliable number; very high-rep sets give rough estimates only.
- Program most working sets at 70–85% of your estimated 1RM, and re-estimate every few weeks as you get stronger. When to advance
- Match the load to your goal — strength leans heavier and lower-rep, hypertrophy moderate, endurance lighter. Strength vs hypertrophy
An estimate, not a prescription. Never attempt a true 1RM without warm-up, sound technique, and a spotter. General information only — not medical or personal-training advice.