One-Rep Max Calculator
Estimate the maximum weight you can lift for one repetition using 6 proven formulas — then get a training percentage table.
Lift Details
How the One-Rep Max Calculator Works
Your one-repetition maximum (1RM) is the heaviest weight you can lift for a single repetition with proper form. It's the foundation of percentage-based strength training — every serious program prescribes working weights as a percentage of your 1RM.
Rather than risking injury with a true maximal attempt, this calculator estimates your 1RM from a submaximal set. Enter the weight you lifted and how many reps you completed, and six well-established formulas produce an estimate. The calculator averages all six for the most reliable number.
The Six Formulas
Epley (1985) uses the formula 1RM = weight × (1 + 0.0333 × reps). It's the most commonly cited in training literature and works best in the 6–10 rep range. Most percentage charts in strength programs are based on Epley.
Brzycki (1993) uses 1RM = weight × 36 / (37 − reps). It tends to be more conservative than Epley and is preferred for low-rep sets (1–6 reps). Epley and Brzycki return nearly identical results at 10 reps but diverge at lower rep counts.
Lombardi (1989) uses an exponential approach: 1RM = weight × reps^0.10. It produces slightly higher estimates than most other formulas and works reasonably well across a wide rep range.
Mayhew et al. (1992) uses a sigmoid curve: 1RM = 100 × weight / (52.2 + 41.9 × e^(−0.055 × reps)). Research by Ware et al. (1995) found it among the most accurate for higher rep ranges (9–20 reps).
O'Conner et al. (1989) uses a simple linear model: 1RM = weight × (1 + 0.025 × reps). It's the most conservative formula and often recommended for beginners as a safe starting point for programming.
Wathen (1994) uses 1RM = 100 × weight / (48.8 + 53.8 × e^(−0.075 × reps)). Published in the NSCA's Essentials of Strength Training, it was found by LeSuer et al. (1997) to be one of the two most accurate formulas overall.
Using the Percentage Table
Once you have your estimated 1RM, the percentage table converts it into practical training weights. Standard training zones:
- Strength (85–100%) — 1–5 reps per set. Builds maximal force production.
- Hypertrophy (65–80%) — 8–12 reps per set. Maximizes muscle growth.
- Endurance (50–65%) — 15+ reps per set. Builds muscular endurance and work capacity.
These percentages are guidelines. Individual variation in muscle fiber composition and training experience means your actual rep counts at a given percentage may differ.
Tips for Accurate Estimates
- Use 3–6 reps for the most accurate estimate. This range balances signal (strength) to noise (fatigue).
- Rest fully before your estimation set — 3–5 minutes between sets.
- Strict form only. Sloppy reps inflate the rep count artificially.
- Compound lifts work best. These formulas were developed using squat, bench press, and deadlift data.
- Average multiple data points. Your estimated 1RM from 100 kg × 5 and from 90 kg × 8 should be similar. If they diverge, investigate why.
Frequently Asked Questions
How accurate are 1RM calculators?
Most formulas are accurate within 5% when using 2–10 reps. Accuracy drops above 10 reps because fatigue and endurance dominate. For best results, use a weight you can lift 3–6 times with strict form.
Which 1RM formula is best?
No single formula is universally best. Epley works well for 6–10 reps, Brzycki for 1–6 reps. Research found Mayhew and Wathen most accurate overall. Using the average of all six gives the most reliable estimate.
Should I test my actual 1RM?
Testing a true 1RM carries injury risk and requires proper warm-up, spotters, and technique. Estimation from submaximal sets is safer and sufficient for programming training percentages. Save true maxing for competition prep.
How do I use the percentage table?
The table shows training weights for different rep ranges. For strength (1–5 reps), use 85–100% of your 1RM. For hypertrophy (8–12 reps), use 65–80%. For endurance (15+), use 50–65%. Adjust based on how the weight feels.