One Rep Max Calculator
Estimate your maximum strength for any lift using 6 science-backed formulas. Get your full training zone breakdown instantly.
Your Lift Details
Enter the weight and reps you completed in your working set.
Most accurate with 3–10 reps. Accuracy drops above 10 reps.
Enter weight and reps
Your estimated 1RM and training zones appear instantly
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The one rep max (1RM) calculator estimates the maximum weight you can lift for a single repetition on any exercise, based on a sub-maximal working set. This approach is safer and more practical than attempting a true 1RM, especially for everyday gym-goers without a spotter. The calculator uses six of the most validated formulas in exercise science and displays their average for the most accurate result.
How 1RM Estimation Works
All six formulas use the same two inputs — the weight you lifted and the number of reps you completed — and apply different mathematical relationships to back-calculate the theoretical maximum. The formulas produce slightly different values; the average across all six reduces individual formula bias and gives a more reliable central estimate.
| Formula | Equation | Best For |
|---|---|---|
| Epley (1985) | w × (1 + r/30) | General use, widely validated |
| Brzycki (1993) | w × 36 / (37 − r) | 3–10 rep range |
| Lander (1985) | w × 100 / (101.3 − 2.67123 × r) | Broad range accuracy |
| Lombardi (1989) | w × r^0.10 | Higher rep ranges |
| Mayhew et al. (1992) | w × 100 / (52.2 + 41.9 × e^(−0.055 × r)) | 10+ rep sets |
| O'Conner et al. (1989) | w × (1 + 0.025 × r) | Conservative estimate |
Training Zones Based on Your 1RM
Once you know your 1RM, you can set precise training loads for any goal. This is the foundation of percentage-based programming (also called "percentage-based training" or PBT):
- 55–65% 1RM — Muscular Endurance: High reps (15–25+), builds aerobic capacity in muscle, improves work capacity. Used in circuit training and GPP phases.
- 65–75% 1RM — Hypertrophy/Volume: Moderate reps (10–15), maximizes time under tension and metabolic stress. Common in bodybuilding-style training.
- 75–85% 1RM — Strength-Hypertrophy: Medium reps (6–10), the sweet spot for building muscle and strength simultaneously.
- 85–95% 1RM — Strength: Low reps (2–5), trains the nervous system to recruit maximum muscle fibers. Core of powerlifting programs.
- 95–100% 1RM — Maximal Strength: Singles and doubles, used in peaking phases before competition. High injury risk — requires advanced technique.
How to Perform a Sub-Maximal 1RM Test
Follow this protocol for the most accurate estimate:
- Warm up with 5–10 minutes of light cardio followed by dynamic mobility work for the target joint.
- Perform 2–3 warm-up sets: 40% of estimated max for 8 reps, 60% for 5 reps, 75% for 3 reps. Rest 2 minutes between each.
- Select a weight you expect to lift 3–6 times. Perform the set stopping with 0–1 reps in reserve (RIR).
- Enter the weight and completed reps into this calculator. Your estimated 1RM is displayed instantly.
- Rest at least 5–10 minutes before attempting any heavy sets on the same movement.
Frequently Asked Questions
Your one rep max (1RM) is the maximum amount of weight you can lift for a single repetition with proper form for a given exercise. It is the gold standard for measuring absolute strength and is used to set training loads across all rep ranges. You should never attempt a true 1RM without a spotter and adequate warm-up.
Estimated 1RM formulas are most accurate when using sets performed in the 3–10 rep range. The accuracy decreases significantly above 10 reps because muscular endurance begins to play a larger role than raw strength. Research shows that estimates from 3–5 rep sets are typically within 2–5% of the true 1RM for most people.
The Epley and Brzycki formulas are the most widely used and validated for sets of 1–10 reps. Mayhew et al. performs well for sets closer to 10 reps. The Lander formula is considered reliable across a broad range. For practical purposes, taking the average of all formulas — as this calculator does — provides the most robust estimate.
Training zones based on 1RM: 55–65% for muscular endurance (12–20+ reps), 70–80% for hypertrophy/muscle growth (8–12 reps), 80–90% for strength development (4–6 reps), and 90–100% for maximum strength and power (1–3 reps). Most programs cycle through these zones rather than staying in one range permanently.
For beginners, re-testing or re-estimating your 1RM every 4–6 weeks is reasonable as strength gains are rapid. For intermediate and advanced lifters, every 8–12 weeks is more appropriate. Rather than testing true 1RM frequently (which carries injury risk), use sub-maximal test sets (3–5 reps to near failure) to estimate your current 1RM safely.
Yes — the 1RM formulas are exercise-agnostic and work for any single-joint or compound movement: squat, bench press, deadlift, overhead press, barbell row, leg press, and more. However, isolation exercises like bicep curls or lateral raises are rarely tested for 1RM. This calculator is most commonly used for the major compound barbell lifts.
No. You do not need to train to absolute failure. You need to perform a set with a known weight and stop when you feel you have 0–1 reps remaining in the tank (RIR 0–1). Using a weight you can lift 3–5 times near your limit gives a reliable estimate without the fatigue and injury risk of true maximal testing.