Σ Smart Calculators
Free · No sign-up required

One Rep Max Calculator

Estimate your one-rep max from any set of 1–15 reps. Get your 1RM across 5 proven formulas plus a full training percentage table.

1RM inputs

This calculator is for informational purposes only and is not a substitute for professional medical advice. Consult a qualified healthcare provider before making changes to your diet, exercise, or health regimen.

What is a one-rep max and why does it matter?

Your one-rep max (1RM) is the maximum weight you can lift for a single repetition of a given exercise with proper form. It is the universal benchmark of absolute strength and the foundation of percentage-based training programs like Wendler 5/3/1, Starting Strength, and nSuns.

Knowing your 1RM lets you set training loads precisely. Instead of guessing, you work at specific percentages — 70% for hypertrophy, 85% for strength, 95% for peaking — which ensures progressive overload without excessive fatigue or injury risk.

How this calculator works

Rather than actually maxing out (which requires spotters, experience, and carries injury risk), this calculator estimates your 1RM from a sub-maximal set. You enter the weight you lifted and how many reps you completed, and we apply five established prediction formulas:

  • Epley (1985): 1RM = w × (1 + r/30). Simple, widely used, works well for 1–10 reps.
  • Brzycki (1993): 1RM = w × 36/(37 − r). Very close to Epley below 10 reps, diverges above.
  • Lombardi (1989): 1RM = w × r^0.10. Uses a power function; tends to give slightly lower estimates.
  • O'Conner et al.: 1RM = w × (1 + 0.025 × r). Linear and conservative.
  • Mayhew et al. (1992): 1RM = 100w / (52.2 + 41.9 × e^(−0.055r)). Exponential model based on bench press data.

We show all five results plus their average. The average smooths out individual formula biases and gives you the most robust single number to base your training on.

Worked example

You bench press 100 kg for 5 reps:

  • Epley: 100 × (1 + 5/30) = 100 × 1.167 = 117 kg
  • Brzycki: 100 × 36/32 = 113 kg
  • Lombardi: 100 × 5^0.10 = 100 × 1.175 = 117 kg
  • O'Conner: 100 × (1 + 0.125) = 113 kg
  • Mayhew: 10000 / (52.2 + 41.9 × 0.760) = 10000 / 84.04 = 119 kg
  • Average: 116 kg

Your estimated 1RM bench press is approximately 116 kg. At 80% (hypertrophy range), you would train with about 93 kg for sets of 8–10.

How to use training percentages

The percentage table translates your 1RM into practical training loads:

  • 90–100%: Max-effort singles and doubles. Peaking and testing.
  • 80–90%: Heavy strength work. Sets of 3–6. This is where most "strength programs" live.
  • 70–80%: The hypertrophy sweet spot. Sets of 8–12 with moderate load build muscle most efficiently.
  • 60–70%: Lighter hypertrophy and muscular endurance. Good for accessory work and higher-rep sets.
  • 50–60%: Warm-up, technique practice, rehab, and deload weeks.

Most well-designed programs alternate between these zones across the training week or block. A typical week might include one heavy day (85–90%), one moderate day (70–80%), and one light day (60–70%).

Common mistakes

  • Using too many reps. Formulas are most accurate for sets of 1–6 reps. A 15-rep set tests endurance more than strength, and the 1RM estimate may be 10–15% off.
  • Ignoring form. If you grind out 5 ugly reps, the calculator treats them the same as 5 clean reps. Cheated reps inflate the estimate.
  • Not re-testing. Your 1RM changes as you get stronger. Re-estimate every 4–8 weeks to keep your training percentages accurate.
  • Applying across exercises. A formula calibrated on bench press data may not perfectly predict your squat 1RM. Use exercise-specific data when possible.
  • Treating the number as exact. These are estimates. Your actual 1RM on any given day depends on sleep, nutrition, stress, warm-up, and a dozen other factors. Use the estimate as a guide, not a guarantee.

When to consult a professional

If you are new to lifting, returning from injury, or planning to actually attempt a true 1RM, work with a qualified coach or experienced training partner. A calculator estimates — only you and your body know your actual limits. Ego lifting causes injuries; calculated training prevents them.

Frequently Asked Questions

What is a one-rep max (1RM)?
Your one-rep max is the maximum weight you can lift for a single repetition with proper form. It is the gold standard for measuring absolute strength in a given exercise and is used to program training percentages.
How accurate are 1RM formulas?
Most formulas are accurate to within ±5% for sets of 1–6 reps. Accuracy decreases beyond 10 reps because fatigue, form breakdown, and muscular endurance start to dominate over raw strength. Always use a moderate rep range (3–6) for the most reliable estimate.
Which formula is the most accurate?
There is no single "best" formula — accuracy depends on the exercise, the lifter, and the rep range. Epley and Brzycki tend to agree below 10 reps. We show 5 formulas and their average to give you a robust estimate.
Should I actually attempt a 1RM lift?
Not necessarily. True 1RM testing requires excellent form, a proper warm-up protocol, spotters, and experience. For most recreational lifters, a calculated estimate from a 3–5 rep set is safer and sufficient for programming.
How do I use training percentages?
Once you know your 1RM, you can program training loads: 70–80% for hypertrophy (8–12 reps), 80–90% for strength (3–6 reps), 90–100% for peaking. Most programs like 5/3/1, Starting Strength, and nSuns are built on percentage-based training.
How often should I re-test my 1RM?
Every 4–8 weeks is typical for intermediate lifters. Beginners progress fast enough to re-test every 2–4 weeks. Advanced lifters may only test every 12+ weeks during peaking cycles. Use the calculator with a recent set rather than maxing out every session.
Does this work for all exercises?
These formulas were developed primarily for compound barbell lifts (squat, bench press, deadlift, overhead press). They are less reliable for isolation exercises, machines, or bodyweight movements where technique and leverage differ significantly.
Why does Brzycki diverge at high reps?
The Brzycki formula has a denominator of (37 − reps), which approaches zero as reps approach 37, making the estimate explode. Above 10 reps it becomes increasingly unreliable. This is why we cap input at 15 reps and recommend using 3–6 reps for the best estimate.