Compare six common 1RM formulas side by side: Epley, Brzycki, Lombardi, Mayhew, O'Conner, and Wathen. Use the spread and average as a practical estimate range.
No single 1RM formula works best in every rep range or lifter population.
This calculator applies several common equations side by side and shows an average so you can see a reasonable estimate band instead of relying on one formula alone.
Use it as a comparison tool for training decisions rather than a replacement for a tested max.
It is useful when you want more context than a single equation can provide. Seeing the spread across formulas is often more informative than treating any one estimate as exact.
Six formulas compared: • Epley: weight × (1 + reps/30) • Brzycki: weight × 36/(37 − reps) • Lombardi: weight × reps^0.10 • Mayhew: weight × 100/(52.2 + 41.9 × e^(−0.055 × reps)) • O'Conner: weight × (1 + 0.025 × reps) • Wathen: weight × 100/(48.8 + 53.8 × e^(−0.075 × reps)) Best estimate = average of all six formulas
Result: Average 1RM: ~259 lbs | Range: 253–264 lbs across six formulas
For 225 lbs × 5 reps: Epley = 262.5, Brzycki = 253.1, Lombardi = 264.3, Mayhew = 261.2, O'Conner = 253.1, Wathen = 260.8. Average: ~259 lbs. The 11.2-lb range (253–264) represents 4.4% variability — typical for 5-rep sets. This close agreement suggests the formulas are pointing to a similar estimate.
A 2012 meta-analysis published in the Journal of Strength and Conditioning Research compared seven 1RM prediction formulas across hundreds of tests. No single formula was most accurate for all exercises, rep ranges, or populations. However, the average of multiple formulas consistently fell within 3-5% of actual 1RM, regardless of conditions. This finding supports the multi-formula approach used in this calculator.
The six formulas fall into three mathematical families. Linear (Epley, O'Conner): predict 1RM increases at a constant rate per additional rep. Simple and accurate at low reps but overestimate at high reps. Hyperbolic (Brzycki): 1RM prediction accelerates with each additional rep, producing conservative estimates at moderate reps. Power/Exponential (Lombardi, Mayhew, Wathen): model the diminishing relationship between reps and strength using curves that naturally level off, producing more realistic predictions at higher reps.
Once you have your estimated 1RM, use percentage-based programming: Warm-up sets (40‒60%): Activate muscles and groove the movement pattern. Working sets depend on your goal — strength (80‒95%), hypertrophy (60‒80%), or endurance (40‒60%). Most proven programs (5/3/1, Starting Strength, Juggernaut, GZCL) are built around percentages of 1RM. Update your training max regularly to keep progression on track.
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This worksheet compares several common 1RM equations side by side and uses the spread as a practical estimate band. It is a planning aid for submaximal sets, not a replacement for a tested max.
No single formula is universally most accurate. Accuracy depends on rep range, exercise, and individual factors. Epley and Brzycki are among the most widely used. Lombardi tends to be more forgiving at higher reps. Wathen and Mayhew use exponential curves that model fatigue differently. The average of all six often lands within about 3–5% of actual 1RM for common testing ranges.
Each formula makes different mathematical assumptions about the rep-max relationship. Epley uses a linear model, Brzycki a hyperbolic model, Lombardi a power law, and Mayhew/Wathen use exponential decay. They were also calibrated on different populations (athletes, recreational lifters, etc.) and different exercises.
For general training programming, yes — the average is the most robust estimate. However, for competition preparation (powerlifting, weightlifting), many coaches prefer the more conservative Brzycki estimate to avoid overloading. For testing your actual max, the average gives you a target to work toward.
Not all exercises are safe or practical for 1RM testing. Compound barbell exercises (squat, bench, deadlift, overhead press) are standard for 1RM testing. Avoid testing maxes on exercises with high injury risk (behind-the-neck press) or those limited by stabilizer muscles rather than prime movers (dumbbell flyes, leg extensions at very heavy weights).
Warm up thoroughly (10–15 minutes). Do progressive sets: ~50% × 8, ~60% × 5, ~70% × 3, ~80% × 2, ~85% × 1, ~90% × 1, then small jumps (2–5%) toward your target max. Rest 3–5 minutes between attempts above 85%. Stop if form breaks down. Having a qualified spotter is essential.
Multi-formula averages are typically within 3–5% of actual 1RM for trained lifters using 2–10 reps. This means a predicted 300 lb 1RM could actually be 285–315 lbs. Accuracy decreases with: untrained individuals, reps above 10, isolation exercises, and exercises the lifter rarely performs. Despite these limitations, even imperfect estimates are useful for programming.