7 One Rep Max Formulas Compared: Epley vs Brzycki vs Lombardi

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TL;DR: No single 1RM formula wins everywhere. Epley is the most validated for squats and general use, Brzycki edges it on low-rep bench press sets, and Mayhew performs best on moderate-rep bench sets. Above 10 reps the formulas diverge wildly — a 32.5 kg spread from the same input. The most defensible single number is the average of all seven, which is why our one rep max calculator shows it by default.
A note on units: examples below use kilograms because the research literature does — the formulas are unit-agnostic and work identically in pounds. Just enter lb and read lb out.

Why Does Every 1RM Calculator Give a Different Answer?

Each calculator uses a different prediction equation, and there are seven major ones — developed by sports researchers between 1985 and 1994 as submaximal alternatives to risky maximal testing. Every formula takes the same two inputs (weight × reps) and returns an estimated 1RM. All seven were validated head-to-head in LeSuer et al. (1997) on 67 subjects across bench press, squat, and deadlift.

The 7 Formulas at a Glance

FormulaYearEquationTypeBest validated for
Epley1985w × (1 + r/30)LinearSquat, general use
Brzycki1993w × 36/(37 − r)RationalBench press, 1–5 reps
Lander1985100w/(101.3 − 2.671r)RationalModerate rep ranges
Lombardi1989w × r^0.10PowerHigh reps, conservative
Mayhew1992100w/(52.2 + 41.9e^−0.055r)ExponentialBench press, 5–12 reps
O’Conner1989w × (1 + r/40)LinearConservative floor
Wathan1994100w/(48.8 + 53.8e^−0.075r)ExponentialBalanced all-rounder

Reading the “type” column: linear formulas add a fixed percentage per rep (Epley 3.33%, O’Conner 2.5%). Rational formulas divide by a shrinking denominator — conservative at low reps, explosive and unreliable above 10–12. Lombardi’s power function grows slowest at high reps. The exponentials (Mayhew, Wathan) are the most stable at high rep counts.

What Do the 7 Formulas Say for the Same Lift?

From the exact same set — 100 kg × 5 reps:

Formula1RM estimate
Epley116.7 kg
Brzycki112.5 kg
Lander113.7 kg
Lombardi117.5 kg
Mayhew119.0 kg
O’Conner112.5 kg
Wathan116.6 kg
Average of all 7115.5 kg

The spread at 5 reps is 6.5 kg — manageable. But watch what happens as reps climb:

RepsLowestHighestSpread
5112.5 (Brzycki/O’Conner)119.0 (Mayhew)6.5 kg
10125.0 (O’Conner)134.7 (Wathan)9.7 kg
12128.2 (Lombardi)144.4 (Lander)16.2 kg
15131.1 (Lombardi)163.6 (Brzycki)32.5 kg

At 15 reps the spread hits 32.5 kg — a programming-critical discrepancy. Rule: when the spread exceeds ~10 kg, trust no single formula; retest with a heavier 3–5 rep set. Imperial check (225 lb × 5): Epley gives 262.5 lb, Brzycki 253.1 lb — a 9.4 lb gap that matters on a heavy single.

Epley vs Brzycki: Which Is Better?

Epley (1985) is the most widely used equation, features in the NSCA’s Essentials of Strength Training and Conditioning, and was the most accurate formula tested on Division I football players’ squats (+2.7 kg mean error on 3-rep loads; lowest absolute squat error in LeSuer 1997, ~3%). Brzycki (1993) is the research community’s favorite for bench press — more conservative at low reps, second-most accurate in that same D-I study (−3.1 kg on 5-rep loads).

The 10-rep crossover: Epley and Brzycki produce the identical number at exactly 10 reps. Below 10, Epley reads slightly higher; above 10, Brzycki runs hotter and turns unstable past ~12 reps as its denominator (37 − r) collapses. The 1-rep honesty test: feed in 100 kg × 1 — Brzycki and Lombardi return exactly 100 kg, while Epley overshoots to 103.3 kg and Mayhew to 108.9 kg.

The bigger lesson: in the D-I study both predicted better from 3-rep loads than 5-rep loads. Rep count matters more than formula choice — a 3-rep set through any formula beats a 10-rep set through the “best” one.

What About the Other Five Formulas?

Lombardi (1989) — power function, slowest growth at high reps, most conservative past 10. Your reality check when others give suspiciously big numbers. Mayhew (1992) — exponential, calibrated on bench press subjects; highest at low reps, best for bench 5–12. O’Conner (1989) — most conservative linear (+2.5%/rep); the safe floor for new blocks or post-injury. Wathan (1994) — exponential all-rounder, tracks Epley within a couple kg at every rep count. Lander (1985) — Brzycki’s twin, slightly higher at moderate-high reps; same >12-rep warning.

Which Formula Should You Use?

Your situationUse thisWhy
Bench press, 1–5 repsBrzyckiBest validated at low reps
Bench press, 6–12 repsMayhewCalibrated on bench subjects
Squat / lower bodyEpleyLowest error in testing (~3%)
Any lift, any repsAverage of all 7Cancels each formula’s bias
High-rep set (10+)Lombardi or WathanOnly bounded formulas stay plausible
New block / post-injuryO’ConnerMost conservative — safe floor
DeadliftAny, then add 5–10%All seven underestimate deadlift

Why Does the Average of All 7 Beat Any Single Formula?

Each formula is one vote, not a verdict — simplified models fit decades ago, not laws of physics. The average cancels systematic bias: Epley’s linear optimism offsets O’Conner’s caution, and no single quirk dominates. From 100 kg × 5, the seven span 112.5–119.0 kg; the average (115.5 kg) sits mid-range without requiring you to know which formula fits your situation. That’s why our one rep max calculator computes all seven and leads with the average.

Once you have your number, plug it into the 1RM percentage chart to build training weights — and for the full reliability story, read how accurate 1RM calculators really are.

Frequently Asked Questions

What is the most accurate 1RM formula?
No single formula wins everywhere. Epley is most validated for squats (~3% error), Brzycki edges it on low-rep bench, Mayhew on moderate-rep bench. The average of all seven is the most defensible single number.
Epley or Brzycki — which is better?
They agree exactly at 10 reps. Below 10 Epley reads slightly higher; above 10 Brzycki runs hotter and destabilizes past ~12 reps. For 2–10 rep sets both are excellent.
Why do different calculators show different 1RMs?
Different formulas. From 100 kg × 5 reps the seven range 112.5–119.0 kg (6.5 kg spread); at 15 reps the spread hits 32.5 kg.
Which 1RM formula is most conservative?
O’Conner at moderate reps (+2.5%/rep) and Lombardi at high reps (slowest-growing curve). Use these for the safest possible estimate.
Can I trust a 1RM estimate from a 15-rep set?
No — the formulas disagree by 32.5 kg at 15 reps. Treat it as a rough floor and retest with a heavier 3–5 rep set.
Why does Epley overestimate at 1 rep?
Its linear form adds 1/30 per rep even at r = 1, returning 103.3 kg from a 100 kg single (~3% overshoot). Only Brzycki and Lombardi return exactly your input at one rep.

References

  • Epley, B. (1985); Brzycki, M. (1993); Lombardi, V. (1989); Mayhew, J.L. et al. (1992); O’Conner, B. et al. (1989); Wathan, D. (1994); Lander, J. (1985) — original 1RM prediction equations.
  • LeSuer, D.A. et al. (1997) — simultaneous validation of all seven formulas (bench, squat, deadlift), J. Strength Cond. Res.
  • Reynolds, J.M. et al. (2006) — 5RM input explains 99.3% of variance in bench press 1RM.
  • Stone, M.H. & O’Bryant, H.S. (1987); Arnold, M.D. et al. (1995); Ware, J.S. et al. (1995) — heavier estimation loads predict better.
  • National Strength and Conditioning Association — Essentials of Strength Training and Conditioning.

Last updated October 18, 2026. For general educational purposes only — not medical advice. Consult a qualified coach before heavy resistance training.

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Daved
Strength training writer and SEO specialist. I build calculators and guides for lifters who want numbers they can actually program from — tested against the research, written from the gym floor.

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