One Rep Max Calculator
Estimate your one rep max (1RM) from any submaximal set. Get results from six validated formulas (Epley, Brzycki, Lombardi, Lander, O'Conner, Wathan), a chart comparison, and a full training percentage table — all for free.
What Is One Rep Max (1RM)?
One rep max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with proper form. It's the gold standard for measuring maximal strength and is used to set training loads, track progress, and program strength and hypertrophy workouts.
Testing your true 1RM directly is demanding and carries injury risk. Instead, most lifters estimate it from a submaximal set (e.g. 5 reps at 80 kg) using validated formulas. This calculator does that automatically using six different formulas and shows both each individual result and their average.
The Six 1RM Formulas Used
Epley (1985) — most widely used:
1RM = w × (1 + r / 30)
Brzycki (1993) — classic and accurate for 1–10 reps:
1RM = w × 36 / (37 − r)
Lombardi (1989) — power-based:
1RM = w × r0.10
Lander (1985) — regression-based:
1RM = (100 × w) / (101.3 − 2.67123 × r)
O'Conner et al. (1989) — linear approximation:
1RM = w × (1 + 0.025 × r)
Wathan (1994) — exponential regression:
1RM = (100 × w) / (48.8 + 53.8 × e−0.075 × r)
Where w = weight lifted and r = reps performed.
All formulas are most accurate for 1–10 reps. Above 10 reps, the estimate becomes increasingly unreliable because muscular endurance (not maximal strength) starts to dominate the performance.
Why Use This 1RM Calculator?
- Six formulas at once: Compare results and see how much they agree.
- Average 1RM: A robust value that smooths formula-specific quirks.
- Chart comparison: A bar chart shows how each formula's estimate differs.
- Training loads table: Every percentage of your 1RM with estimated reps and typical use — perfect for programming.
- Safe estimation: No need to perform a risky true 1RM test.
- Free & Private: No registration, no data storage.
How to Use Your 1RM for Training
- Strength (85–95% of 1RM, 1–6 reps): Heavy loads, low reps, longer rest. Builds maximal force.
- Hypertrophy (70–85% of 1RM, 6–12 reps): Moderate loads, moderate reps. Primary driver of muscle growth.
- Muscular endurance (60–70% of 1RM, 12–20+ reps): Light loads, high reps. Improves work capacity.
- Power (30–60% of 1RM, 1–5 reps, explosive): Submaximal loads moved as fast as possible.
Use the training loads table above to find the right weight for any given rep target. Most strength programs use percentages of 1RM rather than fixed weights, so knowing your 1RM lets you follow any program.
Understanding Your Results
- Formula agreement: When all six formulas fall within a few percent of each other, the estimate is more reliable.
- Low reps (1–5): All formulas are reliable — differences are usually under 2%.
- Mid reps (6–10): Formulas start to diverge — Brzycki tends to run slightly higher, Epley slightly lower.
- High reps (11–20): Estimates become less reliable — treat them as rough guides.
Note: These formulas were derived from different populations and exercises. They are most accurate for compound barbell lifts (squat, bench, deadlift, overhead press). For isolation exercises or assistance work, treat the estimate as approximate.
❓ One Rep Max Calculator FAQ
What is one rep max (1RM)?
One rep max is the maximum weight you can lift for a single repetition with proper form. It's the standard measure of maximal strength and is used to set training loads for strength, hypertrophy, and power programs.
Which 1RM formula is the most accurate?
Brzycki and Epley are the most widely validated, especially for 1–10 reps. For very low reps (1–5), all six formulas give nearly identical results. The average of all six (default in this calculator) is the most robust estimate.
How many reps should I use for an accurate estimate?
Best accuracy is with 1–5 reps. 6–10 reps are still reliable but start to diverge. Above 10 reps, the estimate becomes unreliable because muscular endurance dominates. Keep reps at or below 10 for the best estimate.
Do I need a spotter to test my 1RM?
Yes — if you want to test your true 1RM, always use a spotter for safety, especially on bench press. For most lifters, estimating 1RM from a submaximal set (as this calculator does) is safer and just as useful.
Is 1RM different for men and women?
The 1RM formulas themselves do not use gender — only weight and reps. However, men and women differ in absolute strength due to body composition and muscle mass. The gender toggle is provided for reference but does not change the calculated 1RM.
How often should I re-test my 1RM?
Re-test every 4–8 weeks, or at the end of each training block. More frequent testing can hinder progress and increase injury risk. You can also track progress by beating your estimated 1RM from a fixed rep set.
Can I use 1RM estimates for all exercises?
1RM formulas are most accurate for compound barbell exercises like the squat, bench press, deadlift, and overhead press. For isolation exercises (curls, lateral raises), the estimate is less reliable — treat it as a rough guide.
What percentage of 1RM should I train with?
It depends on your goal: 85–95% for pure strength, 70–85% for hypertrophy, 60–70% for endurance, and 30–60% for explosive power. The training loads table above gives you exact weights at every percentage.
Why do different formulas give different results?
Each formula was derived from a different population using different regression techniques. For low reps (1–5), differences are tiny (under 2%). For higher reps, differences widen as the formulas extrapolate further from the tested data.
What is the difference between 1RM and training max (TM)?
Training max is typically 90% of your true 1RM. Programs like 5/3/1 use a training max to ensure you're always working below your absolute limit, reducing injury risk and allowing consistent progress.
Can I estimate 1RM from a set to failure?
Yes — a set taken to technical failure gives the most accurate estimate. Stop 1 rep short of failure only if your form breaks down. Never sacrifice form for reps, especially on heavy sets.
How do I convert measurements between metric and imperial?
This calculator automatically handles both kilograms and pounds. Simply select your preferred unit system, enter your weight, and the calculator uses it consistently for all results.