One-Rep Max Calculator

How a one-rep max is estimated

A one-rep max is the heaviest load you can move through a full range of motion once, and the only way to know it is to attempt it. Everything on this page is the alternative: take a set you have already completed and work backwards along the curve relating load to repetitions. That curve is well documented, because the more weight on the bar the fewer times you can move it, but its exact shape has never been settled, which is why four equations exist rather than one.

All four take the same two inputs and differ only in the function they fit between them. Epley is linear. Brzycki is linear in the denominator, which is a very different thing. Lombardi is a power curve. Wathen is exponential and asymptotic. None of them knows which lift you performed, how close to failure you were, or how long you have trained.

Notice that the weight never needs converting. Each equation multiplies or divides the load you entered by a number derived from reps alone, so the units cancel: kilograms in gives kilograms out, pounds in gives pounds out, and the estimate is identical either way. The switch above changes the label and converts what you typed. It does not change the arithmetic.

Sources: Epley B, Poundage Chart, Boyd Epley Workout, Body Enterprises, Lincoln, Nebraska (1985); Brzycki M, "Strength Testing — Predicting a One-Rep Max from Reps-to-Fatigue", Journal of Physical Education, Recreation & Dance 64:88–90 (1993); Lombardi VP, Beginning Weight Training, William C. Brown, Dubuque, Iowa (1989); Wathen D, "Load Assignment", in Baechle TR (ed.), Essentials of Strength Training and Conditioning, Human Kinetics (1994).

Why the four disagree, and when

The disagreement is structural rather than random, and it tells you how much to trust the answer. Below is what each equation predicts from the same 100 kg lift at four rep counts.

Read the bottom row first. From a triple or a set of five, the four equations sit within about 5 kg of each other, roughly 5% of the answer. By ten reps the gap is nearly 9 kg, and by fifteen it is 32.6 kg: the same set supports a maximum anywhere between 131 kg and 164 kg depending on whose paper you open. At that point the calculator is measuring the disagreement between four authors rather than your strength.

What each curve does at the extremes

Brzycki breaks most dramatically. Its denominator, 1.0278 − 0.0278r, shrinks as reps rise and reaches zero at about 37 reps, where the equation predicts an infinite maximum. It is the most conservative of the four below eight reps and the most aggressive above twelve. That is a strange pair of properties, and a direct consequence of putting the linear term underneath the division.

Epley tracks Brzycki closely at low reps, a few kilograms above it, and the two cross at almost exactly ten. In the table they land within 0.1 kg of each other. Above that they separate, because Epley is a straight line with no upper bound, adding 3.3% of the lifted weight for every extra rep indefinitely. Lombardi is the outlier in the other direction: raising reps to the power of 0.10 flattens the curve hard, so ten reps to fifteen adds only about 5 kg. It reads highest of the four at three reps and lowest by ten.

Wathen holds up best through the middle of the range, sitting close to the average from four reps through twelve. Its exponential form is bounded: as reps climb, the estimate approaches roughly 2.05 times the weight lifted and stops. That is a more physiologically sensible shape than a straight line, or than a formula with a zero in its future.

The conclusion holds whichever equation you prefer: a heavy set of two to five reps is the best input you can give this calculator. In that band all four agree to within a few percent, so the choice between them stops mattering and the estimate rests on the quality of your set rather than the shape of somebody's curve.

Accuracy, and where it misleads

Rep-max equations were fitted to groups and describe groups well. Applied to one person on one day they carry several distinct sources of error.

Rep count is the dominant variable. Estimates are most reliable from sets of two to five and degrade steadily above about ten. The reason is physiological rather than mathematical. A set of three is limited by how much force you can produce; a set of fifteen is limited by local muscular endurance and eventually by cardiovascular capacity. Those qualities vary enormously between people and relate only loosely to maximal strength. Two lifters with an identical one-rep max can differ by five or six reps at 75% of it.

The relationship differs by lift. These equations track well on the squat, bench press and deadlift, where a large amount of muscle works against a load that can be increased in small steps. They track poorly on isolation work and on machines: a curl or a lateral raise involves a small muscle group with a sharp drop-off in force, so rep capacity at a given percentage runs lower than the table predicts. The deadlift is its own case, since grip and lower-back endurance often fail before the prime movers do.

Training history shifts the whole curve. Trained lifters typically manage fewer reps at a given percentage than novices, which is counter-intuitive until you see why: an experienced lifter expresses a higher fraction of their true maximum in a single attempt, so their 1RM sits closer to their heavy-set performance and there is less room left underneath it. A novice's tested single usually understates what their body could do.

Proximity to failure changes everything. This is the largest and most commonly ignored source of error. Every equation above assumes the set you entered was carried to genuine failure, meaning a further rep was not available. A set of five with three reps left in reserve is, in effect, a set of eight, and entering it as a five will understate your maximum by roughly the difference between those two rows of the table. The reverse error is rarer but real: a grinding, form-degrading last rep is not the same as a clean one. If you are unsure how close to failure you were, enter a lower rep count from a set you remember clearly.

How to use the percentage table

The table in the results runs from 100% of your estimated max down to 65%, with the rep count each load typically supports. Most structured strength programmes are written in percentages precisely because they let a coach prescribe the same relative effort to a room full of people at different absolute strengths.

As a rough map: work at 85% and above develops maximal strength, in sets of one to five. The 70% to 85% band is where most productive hypertrophy and general strength work lives, in sets of six to twelve. Below 70% you are training muscular endurance, technique and work capacity. The percentages are deliberately not evenly spaced, because the relationship between load and reps is not linear: the step from 95% to 90% buys you two reps, and so does the step from 75% to 70%, across a much larger weight change.

Two cautions. First, percentages compound an estimate: if your 1RM figure is 5% optimistic, every load in the table is 5% too heavy, and the error bites hardest at the top. Second, a true one-rep max is not a constant. It moves day to day with sleep, food, stress, illness and how far into a training block you are. Swings of 5% to 10% over a week are normal, so a percentage prescribed three weeks ago can land as an easy day or an impossible one.

This is why most coaches now pair percentages with a subjective gauge: RPE on a ten-point scale, or reps in reserve, which asks the simpler question of how many more you could have done. A prescription of "5 reps at 80%, stopping with 2 in reserve" survives a bad night's sleep in a way that "5 reps at 80%" does not. Use the table to set the plan and the daily gauge to adjust it. If you are tracking body composition alongside strength, our macro calculator sets protein targets and the TDEE calculator estimates what those sessions cost.

Testing a true max safely

If you decide to test rather than estimate, treat it as its own session. Arrive fresh, not at the end of a hard week. Warm up progressively: general movement first, then the lift itself in ascending singles and doubles with several minutes of rest between attempts, taking bigger jumps early and small ones near the top. A common approach is to work up in roughly 10% steps to around 90% of your expected max, then move in increments of 2.5% or less, arriving at the heavy attempt primed but not tired.

Have a competent spotter for anything you press while lying underneath it, and know how to bail before you need to: dumping a squat backwards onto the pins, tipping a bench press onto the rack, letting go of a deadlift. Set the safety bars at a height that catches the bar without catching you. If your technique changes shape under maximal load (hips shooting up out of a squat, back rounding in a pull), that attempt is the limit of your technique rather than your strength, and pushing past it is where injuries come from.

For most people, none of this is necessary. An estimate from a heavy triple carries almost all of the useful information, costs one working set instead of a whole session, and needs no recovery week afterwards. Competitive lifters test because the sport requires a tested number. Everyone else can programme perfectly well from the figure at the top of this page, checked against how the bar actually feels.

Common questions