One Rep Max Calculator

one rep max = weight × (1 + reps ÷ 30); weight at n reps = one rep max ÷ (1 + n ÷ 30)

weight

The weight you actually lifted, in the base unit this page computes in. Enter it in pounds and it is converted first, so a 225 lb set and a 102.06 kg set produce the same answer — the pound figure is a conversion of the kilogram one rather than a second calculation (kg)

reps

How many times you completed the lift with that weight, counted honestly. The equation assumes the last rep was the last one you could have done — a set stopped two reps short of failure reads as a heavier one rep max than you have, which is the single most common way this estimate goes wrong

30

The Epley constant, which says that each additional repetition shaves roughly one thirtieth off the fraction of your maximum you are lifting. It is why five reps is worth about 1.167 times the weight and ten reps about 1.333 times: the relationship is not linear, and assuming it is would put the estimate low at high reps

one rep max

The estimated maximum for a single repetition, computed directly from the two figures above. It is an estimate, not a measurement: a true one rep max is a set you have performed after a proper warm-up, and this page never asks whether you had one (kg)

training percentage

The share of that maximum you plan to work at, from 100 per cent down. The table below inverts the same equation to answer the question a lifter actually has at the rack — how many reps a given percentage of the estimated maximum should allow — and it is generated from the same formula rather than copied from a separate chart

Use it when you want a working weight rather than a trophy. The number is most useful in the middle of the rep range: a set of three to six reps is close enough to a true maximum that the estimate is worth acting on, and it is where the table's percentages are most reliable. Beyond about ten reps the equation is extrapolating from a set that says more about your endurance than your strength, and the answer drifts upward. Do not use it to test yourself — a genuine one rep max is performed, not predicted, and estimating it lets you skip the part where a heavy single goes wrong. Do not use it to compare yourself with anyone else either, because the same equation applied to two lifters with different training backgrounds gives two differently-biased answers, as the references below show.

1. 100 kg for 5 reps

   1. 5 ÷ 30 = 0.1667, so the set is 1.1667 times the weight
   2. 100 × 1.1667 = 116.7 kg
   3. 116.7 ÷ 0.45359237 = 257.2 lb

   The combination the page opens with. The step to notice is the first one: five reps adds a sixth of the weight, not a fifth, and that is the whole content of the Epley constant. Rounding to 117 kg would be reasonable on a phone and is wrong in a table — the number that goes on the bar is a plate decision, and the point of printing the decimal is that the calculation, not the display, decided it.

2. 100 kg for exactly 1 rep

   1. One completed repetition is the definition of a one rep max, so the estimate is the weight itself
   2. 100 kg stays 100 kg
   3. 100 ÷ 0.45359237 = 220.5 lb

   The cell where the formula is deliberately not applied. Epley would return 103.3 kg here — it treats a single rep as one more estimation point — but you have just performed the thing being estimated, and reporting a lift you completed as 103.3 kg is the most conspicuous error this page could make. The exception is built into the calculator rather than left to the reader, and it is worth knowing about when you read a one rep max from any other source: most of them apply the formula at one rep without saying so.

3. 60 kg for 10 reps

   1. 10 ÷ 30 = 0.3333, so the set is 1.3333 times the weight
   2. 60 × 1.3333 = 80.0 kg
   3. 80.0 ÷ 0.45359237 = 176.4 lb

   Ten reps is where the estimate starts to lean on endurance rather than strength, and the reading is instructive: 60 kg for ten suggests an 80 kg maximum, which is a third more than you actually held. The table's row for ten reps says a working set of ten should sit at 75 per cent of your maximum, so 80 kg and 60 kg agree — but so would a lifter who genuinely maxes at 85 kg and simply fades late in a set. That ambiguity is why ten reps is the practical upper end for acting on the answer.

4. 140 kg for 3 reps

   1. 3 ÷ 30 = 0.1, so the set is 1.1 times the weight
   2. 140 × 1.1 = 154.0 kg
   3. 154.0 ÷ 0.45359237 = 339.5 lb

   Low reps, close to a true maximum, and the case where the estimate is worth planning a session around. It also produces the cleanest arithmetic on the page — three reps is exactly ten per cent — which makes it a useful one to check the calculator against by hand. The 154 kg figure is in kilograms because that is the unit the page computes in; the 339.5 lb beside it is the same weight, and a lifter working in pounds reads the second number rather than converting the first.

An estimated one rep max is not a measured one, and the difference is not small. The equation assumes your set ended at failure and that the last repetition took as long as the first; in practice a set stopped two reps short reads as a heavier maximum than you have, while a set of ten on a day you were tired reads as a lighter one. The percentage relationship itself is not a constant of nature either: it differs between endurance-trained and strength-trained lifters, so the same equation carries a different bias depending on who is using it, and no single number of reps makes that go away. Treat the answer as a starting weight to try, not a fact about your body. Second, this page uses Epley and only Epley. Brzycki and Lombardi are in common use and would give you a different figure — around four per cent apart at ten reps and under two at five — and there is no way for a reader to tell from the page which is closer to their own result. If you need that precision, measure a real maximum. Third, the table stops at twelve reps, and the percentages below that point are the ones to distrust first, because the formula is being asked to describe a set that is mostly endurance. Finally, nothing here accounts for technique, tempo, range of motion or how much of the lift was momentum, all of which can move a set by a rep in either direction.

Which formula does this one rep max calculator use?

Epley's: the weight you lifted multiplied by one plus the number of reps divided by thirty. It is the equation used in the largest share of published comparisons, it is a single line of arithmetic you can check on a phone, and it does not break down at any rep count you can realistically reach. The alternative most often quoted is Brzycki, which is accurate over a similar range but divides by thirty-seven minus the reps — so at thirty-seven reps it has no answer at all, and near it the answer is nonsense.

Why can't I choose a different formula from a dropdown?

Because you would have no way to decide. The common equations agree to within about two per cent at five reps and diverge to around four per cent at ten, which is smaller than the day-to-day variation in your own performance. A dropdown would hand you a choice whose effect you cannot observe, and it would mean the number on the page depended on which option happened to be selected. One equation, stated plainly, is more honest than three you have to arbitrate between.

What if I lifted the weight only once?

Then you have measured your one rep max rather than estimated it, and the calculator returns the weight unchanged. Applying the formula at one rep would inflate a 100 kg lift to 103.3 kg, which is a strange thing to do to a number you just produced with your own hands. This is worth knowing because most online calculators do not make the exception, so a figure you read elsewhere for a single lift may be slightly above what was actually performed.

How do I use the percentage table for a working set?

Find the row for the number of reps you intend to do, take the percentage beside it, and apply it to your estimated maximum. If your estimate is 116.7 kg and you want a set of five, the table's five-rep row reads 85.7 per cent, which is 100.0 kg. The table is the same equation read backwards, so the weight it gives you is the weight the calculator believes you could lift five times — the two will always agree, which is the point of generating one from the other rather than copying a chart.

Is the estimate more accurate at low reps?

Yes, and the reason is arithmetic rather than physiology. At three reps the formula is adjusting your set upward by ten per cent; at ten reps it is adjusting it by a third. A small correction from a slightly wrong assumption stays small, while a large one magnifies it — so a set of two to six reps is where the estimate is worth acting on, and a set of fifteen is mostly telling you about your conditioning.

Can I use this for a squat or a deadlift as well as a bench press?

The arithmetic works the same way, but the accuracy does not. The published comparisons find the equations track measured maxima more closely in the bench press than in the squat or deadlift, where the range of motion and the technical limit tend to make sets end for reasons other than strength. Use the estimate as a starting point for a heavy set and let the set itself correct it, rather than treating a squat number from this page as a tested maximum.

How often should I retest my one rep max?

Retest when the estimate and your training disagree, not on a calendar. If the table says five reps should be 85.7 per cent of your maximum and you are completing eight at that weight, your maximum has moved and the old number is holding you back. A rough guide is every six to twelve weeks of consistent training, and it is usually enough to update the estimate from a hard set rather than performing a true single — the estimate exists precisely so that you rarely have to.

• Evaluation of Load-Velocity Relationships and Repetitions-to-Failure Equations in the Presence of Male and Female Spotters — Nickerson BS, Williams TD, Snarr RL, Garza JM, Salinas G — Journal of Strength and Conditioning Research, 2020;34(9):2427-2433 — a bench press study comparing measured one rep max against three repetitions-to-failure equations, in which the Epley estimate showed the smallest mean difference from the measured maximum and the lowest standard error of the three
• Analyzing one-repetition-max predictions: load-velocity relationship vs. repetition to failure equation in ten lower extremity exercises — Sport Sciences for Health (Springer) — ten lower-body exercises, with the repetition-to-failure equations reporting mean absolute errors around 12 per cent for Epley against 16 per cent for Brzycki, and correlations with the measured maximum near 0.97, which is the range this page's answer sits in
• The relationship between the number of repetitions performed at given intensities is different in endurance and strength trained athletes — Richens B, Cleather DJ — Biology of Sport, 2014;31(2):157-161 — the study behind the point that the reps-to-percentage relationship is not the same for everyone: endurance-trained and strength-trained athletes need different equations to describe the same effort