One Rep Max Calculator

Enter the weight you lifted and how many clean reps you completed with it, and the calculator estimates your one-repetition maximum, or 1RM — the heaviest single lift you could manage. The headline number uses the Epley formula; the table beneath it shows what Brzycki, Lombardi and O'Connor make of the same set, because the four disagree by a few percent and that spread is the honest width of the estimate. A second table converts the Epley estimate into training loads from 95 down to 70 percent of max.

How the four formulas work

All four take the weight lifted w and the repetitions completed r and scale it up by a factor that grows with the rep count. Epley's adds a thirtieth per rep:

1RM = w × (1 + r ÷ 30)

Brzycki's divides instead:

1RM = w × 36 ÷ (37 − r)

Lombardi's is the lone power curve:

1RM = w × r^0.10

and O'Connor's is Epley's shape with a gentler slope, a fortieth per rep:

1RM = w × (1 + r ÷ 40)

The literature usually prints the first two in decimal form, Epley with a 0.033 multiplier and Brzycki as weight over 1.0278 minus 0.0278 times reps, but these are the same equations: 0.033 is a rounded 1/30, and 1.0278 and 0.0278 are rounded 37/36 and 1/36. The equation table in Reynolds, Gordon and Robergs' 2006 comparison lists Brzycki and Epley as valid at ten reps or fewer and Lombardi at eleven or fewer, with no stated limit for O'Connor, and that study found every equation less accurate when fed ten-rep data instead of five-rep data. Treat longer sets as rough; the rep input stops at fifteen, the widest limit in that table, which belongs to the Mayhew equation rather than any of the four here.

A worked example at the defaults

The defaults describe a set of five reps at 185 lb. Epley multiplies 185 by 1 + 5/30, which is 7/6, giving 215.8 lb. Brzycki computes 185 × 36 ÷ 32 = 208.1 lb. Lombardi raises the rep count to the power 0.10 — five to the 0.1 is 1.1746 — and multiplies, giving 217.3 lb. O'Connor gives 185 × (1 + 5 ÷ 40) = 208.1 lb, no rounding coincidence: at five reps Brzycki's 36/32 equals O'Connor's 1.125, the only rep count from two to fifteen where the two agree. The full spread runs from 208.1 to 217.3 lb, about nine pounds or four percent.

From hospital wards to the power rack

Estimating strength from repetitions began in rehabilitation, not sport. In 1945 the U.S. Army physician Thomas L. DeLorme rebuilt injured soldiers by having them lift their ten-repetition maximum, and by 1948 he had refined the protocol into three progressively heavier sets of ten under the name Progressive Resistance Exercise. His 1951 book Progressive Resistance Exercise: Technic and Medical Application and his papers on the method, as Todd, Shurley and Todd's 2012 history puts it, helped legitimize strength training and played a key role in laying the foundation for the science of resistance exercise.

The single maximal lift then became a sport in its own right. Powerlifting evolved from a pursuit known as odd lifts; the first national competition came in September 1964 under the auspices of the York Barbell Company, the first named USA National Championships followed in 1965, and the International Powerlifting Federation formed in November 1972, holding its first world championships the next year.

The formulas came out of the coaching profession that grew up alongside. Boyd Epley became college football's first full-time strength and conditioning coach when Nebraska hired him in 1969, and in 1978 he organized a meeting of 76 strength coaches in Lincoln that led to the National Strength and Conditioning Association. His formula was never a journal paper: it is a poundage chart on page 86 of the 1985 Boyd Epley Workout, a Body Enterprises training manual, formalizing the rep-to-max conversion used to program his athletes. Matt Brzycki published his in 1993 in the Journal of Physical Education, Recreation and Dance. The other two are textbook rules: Lombardi's power curve appeared in his 1989 Beginning Weight Training with, as Reynolds later noted, no data or evidence of data behind it, and O'Connor's comes from Weight Training Today, the 1989 textbook by Bob O'Connor, Jerry Simmons and Pat O'Shea.

How accurate the estimates are

The formulas met serious testing in the 1990s. According to the abstract of LeSuer and colleagues' 1997 comparison, which ran seven prediction equations — these four among them — over 67 untrained college students on the bench press, squat and deadlift, correlations with tested maxes were uniformly above 0.95, and rep counts of ten or fewer predicted 1RM accurately; yet only the Mayhew and Wathan equations, neither of them among the four here, matched bench press maxes without significant error, only Wathan did so for the squat, and every equation significantly underestimated deadlift maxes, a shortfall later accounts put at 22 to 34 pounds, or 9 to 14 percent. A deadlift estimate deserves extra skepticism.

Reynolds, Gordon and Robergs' 2006 leg press and chest press data, from adults of mixed training status, shift the question from formulas to lifts. Their own equation and those of Abadie and Epley had the smallest mean residuals, with a slight tilt to overestimate; Brzycki, Lander and O'Connor all underestimated leg press strength; and the nonlinear Lombardi and Mayhew equations trailed every linear one. For the chest press, though, the most accurate were theirs, Brzycki's and O'Connor's — the same two that fell short on the leg press — which is why the paper concluded prediction equations must be exercise specific.

The cautionary case is Mayhew and colleagues' 2008 study of 103 college women with little lifting experience, tested before and after twelve weeks of training. Their sets averaged 12.5 reps to fatigue, beyond the ten-rep validity window. Across that full range only three of the fourteen equations compared produced predictions significantly different from the measured maxes, and the linear Brzycki and Lander equations were two of the three — also the only ones that stopped tracking measured strength. Every equation did better for women who stayed under ten reps.

Estimates exist because testing a true max is not always wise. As the American Council on Exercise frames it, a predicted 1RM test is the right tool for a novice who lacks adequate experience handling free weights, because an actual max attempt pushes the lifter to his or her limit and is not appropriate for beginners.

Turning the estimate into training loads

The second table converts the Epley estimate into working weights using the percentage pairs from the NSCA training load chart, which matches 100 percent of max with 1 rep, 95 with 2, 90 with 4, 87 with 5, 85 with 6, 80 with 8, 75 with 10 and 70 percent with 12. The chart runs both ways in its own two examples: 160 lb for 8 squat reps is credited with a 200 lb max, and a 200 lb max should yield 10 reps at 150 lb, or 75 percent. It credits its numbers to Landers' NSCA Journal note Maximum based on reps, the source behind the Lander equation the comparison papers keep testing. On a 225 lb bench set of 8, the chart's 80 percent gives 281 lb, between the Epley 285.0 and Brzycki 279.3 estimates for the same set. Built on Brzycki or O'Connor instead of Epley, every load would sit a few percent lower. Treat the pairs as programming conventions, not physiological law; individuals differ in how many reps they complete at a given percentage.

Assumptions and conventions

A set of one is a measured max, so at one rep the calculator returns the entered weight from all four formulas. Brzycki's and Lombardi's algebra does that on its own — 36/36 and 1 raised to any power are both 1 — but Epley's and O'Connor's lines would report 3.3 and 2.5 percent more than a weight already lifted once, so the calculator overrides them there. Lombardi's exponent is 0.10, as the Reynolds 2006 equation table prints it; the 0.13 that turns up in text copied out of the Mayhew 2008 PDF is the exponent 0.1 followed by a multiplication sign the file encodes as a digit 3, not a different formula. The spelling O'Connor follows the byline of the 1989 book, though journal papers often print O'Conner, and the Mayhew 2008 paper uses both. The pound and kilogram switch changes labels only, and weight entries above 2,000 are rejected in either unit. The percentage pairs are chart conventions, not an NSCA endorsement of any of the four formulas.

A predicted max is an estimate, not a guarantee of capability, and maximal lifting carries injury risk — novices should not attempt true one-rep singles without qualified supervision. See the site disclaimer.

Frequently asked questions

How many reps should I use to estimate my one rep max?

Ten or fewer, and fewer is better. The Reynolds 2006 comparison lists the Brzycki and Epley equations as valid at ten reps or fewer and Lombardi at eleven or fewer, found every equation less accurate when built from ten-rep data than from five-rep data, and concluded that of the 5, 10 and 20RM conditions it tested the 5RM predicted best; Mayhew and colleagues' 2008 study of college women likewise found the equations more accurate for lifters who stayed under ten reps. A hard set of two to five reps gives the steadiest estimate; this calculator accepts up to fifteen reps but results above ten should be read as rough.

Which one rep max formula is most accurate?

None wins everywhere, and the winner changes with the lift. According to the abstract of LeSuer and colleagues' 1997 study of 67 untrained college students, all seven tested equations correlated with measured maxes above r = 0.95, yet only the Mayhew and Wathan equations, neither of them among the four here, matched bench press maxes without significant error, only Wathan did so for the squat, and every equation significantly underestimated the deadlift by an average later accounts put at 9 to 14 percent. In the 2006 Reynolds leg press and chest press data, Epley trended slightly high while Brzycki, Lander and O'Connor underestimated leg press strength, yet Brzycki and O'Connor were among the most accurate for the chest press, which is why that paper concluded prediction equations must be exercise specific. That is why this calculator shows four estimates side by side instead of declaring one the answer.

Why do the Epley and Brzycki formulas give different answers?

Each author fitted a different population, lift and rep range, and two of the four formulas were published without any dataset at all. Reynolds and colleagues note that Lombardi's 1989 textbook equation came with no supporting data, and the O'Connor equation likewise comes from a 1989 textbook. At five reps the spread across the four estimates is roughly four percent, which is the honest width of the estimate.

Is it safer to estimate a one rep max than to test it?

For beginners, yes. The American Council on Exercise describes predicted 1-RM tests as the way to estimate maximal strength in a novice who lacks adequate experience handling free weights, because an actual max attempt pushes the lifter to his or her limit and is not appropriate for beginners. An estimate from a submaximal set carries most of the information at far less risk.

What percentage of my 1RM should I lift for 8 reps?

About 80 percent, per the NSCA training load chart, which pairs 1 rep with 100 percent of max, 2 reps with 95, 5 with 87, 8 with 80, 10 with 75 and 12 with 70 percent. The chart's own example runs the same ratio the other way: an athlete who squats 160 pounds for 8 reps is credited with an estimated 200 pound max. The pairs are adapted from Landers' NSCA Journal note Maximum based on reps, and are programming conventions rather than physiological law, since individuals differ in how many reps they complete at a given percentage.

Who invented the one rep max formula?

There is no single inventor. The Epley formula comes from a poundage chart on page 86 of the 1985 Boyd Epley Workout manual, written by the Nebraska strength coach who founded the NSCA in 1978. Matt Brzycki published his version in a 1993 article in the Journal of Physical Education, Recreation and Dance, and the Lombardi and O'Connor formulas both appeared in 1989 weight training textbooks.