One Rep Max Calculator
Estimate your 1RM from a set you already did, with six formulas and how much they disagree.
A one rep max calculator estimates the heaviest weight you could lift once, based on a set you have already completed. The Epley formula is weight x (1 + reps/30), so 100 kg for 5 reps gives about 117 kg. This tool runs six published formulas and reports the median, which for that set is 116.6 kg. Estimates are most reliable from sets of 10 reps or fewer.
This calculator is for general education only and is not medical, training, or physiotherapy advice. Estimates come from published formulas fitted to group data and can differ from your true maximum by 10% or more. Never load a bar based on an estimate without an appropriate warm up, sound technique, and safety equipment or a spotter. If you have an injury or a medical condition, speak to a qualified professional before maximal lifting.
Estimated one rep max
The mean sits below the median, so at least one formula is reading low relative to the rest. The median is what gets the headline either way, because one outlier cannot move it.
All six formulas were fitted on sets around this length, so they are working inside their data rather than reaching past it.
Disagreement between the six
5.8%
Lowest Brzycki 253.1 lb, highest Mayhew 267.8 lb.
The six land close together, which is the main reason the figure above is worth anything.
What each formula says
- Brzycki253.1 lb
- O'Conner253.1 lb
- Wathen262.3 lb
- Epley262.5 lb
- Lombardi264.3 lb
- Mayhew267.8 lb
Six published formulas, lowest first. They were fitted on different groups of lifters, so they disagree by design. How far apart they sit is the most useful thing on this page: agreement is the reason to trust an estimate, and there is no way to see it from one number.
Loads by percentage of the estimate
| Percent | Load |
|---|---|
| 100% | 262.4 lb |
| 95% | 249.3 lb |
| 90% | 236.2 lb |
| 85% | 223.0 lb |
| 80% | 209.9 lb |
| 75% | 196.8 lb |
| 70% | 183.7 lb |
| 65% | 170.6 lb |
| 60% | 157.4 lb |
| 55% | 144.3 lb |
| 50% | 131.2 lb |
Percentages of the median estimate above, so everything in this column inherits whatever the estimate is worth. There is no rep column on purpose: how many reps anyone gets at a given percentage varies by lift, by training history and by the day, and printing that convention beside a number derived a different way would put two models in one answer.
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About the One Rep Max Calculator
A one rep max is the heaviest weight you can lift for a single repetition, and it is the number most strength programs are written around. Testing it directly is time consuming and carries some risk, so it is usually estimated from a set you already did. This tool runs six published formulas at once: Epley, Brzycki, Lombardi, Mayhew, O'Conner and Wathen. It shows all six, because they disagree, and the size of that disagreement tells you how much to trust the answer. The headline figure is the median rather than the average, deliberately. Some of these formulas behave badly at higher rep counts, and one bad estimate can drag an average a long way while the median stays put. You will also see a confidence rating and the spread between the highest and lowest estimate. These are empirical curves, most of them built from bench press data at moderate rep counts, and none was designed for high-rep work. They are at their best from 1 to 10 reps, where the six typically land within about 9% of each other, get noisy through the teens, and by 20 reps the six can be more than 50% apart. Past 20 the tool declines to answer at all rather than print a confident number it does not believe. At exactly one rep, four of the six return more than the weight you actually lifted, from about 1% over up to nearly 9% over on the Mayhew formula, because they are fitted curves rather than definitions. If you genuinely lifted a single, that weight is your max and it beats any estimate here. The percentage table gives you loads only, deliberately. Percentage-of-max programming is the standard approach in strength and conditioning, including in the NSCA's own guidance, but the rep counts a given percentage buys you are a rule of thumb rather than a measured constant. Charts that also tell you how many reps you should get at 80% are quoting a generic convention that varies by lift, by person and by the day, and pairing that convention with a number derived a different way would put two different models in one answer.
Frequently asked questions
How is a one rep max calculated?+
From the weight lifted and the number of reps completed. Epley is weight x (1 + reps/30). Brzycki is weight x 36 / (37 - reps). Lombardi raises the reps to a small power, O'Conner adds a flat 2.5% per rep, and Mayhew and Wathen use exponential decay curves. All of them are fitted to observed data rather than derived from first principles, which is why they disagree.
Which 1RM formula is most accurate?+
It depends on the lift and the rep range, and no single one wins everywhere. Epley and Brzycki are the most widely used and agree closely at low reps. Rather than pick one, this tool shows all six and reports the median plus the spread, so you can see whether they agree, which is the actual signal of reliability.
Why will the calculator not go past 20 reps?+
Because past that these formulas stop meaning anything. Brzycki in particular has a mathematical pole at 37 reps, where it heads toward infinity, and it is producing absurd numbers well before that. At 20 itself you still get a figure, flagged low confidence, with the full spread shown so you can see how little it means: the six estimates can sit more than 50% apart there. Past 20 the tool returns nothing rather than a number from formulas operating far outside the data they were fitted on.
Why is my estimated max higher than a single I actually lifted?+
Because the formulas are fitted curves, and at one rep several of them return a little above the input weight. If you genuinely lifted a single, that weight is your tested max and it beats any estimate. These formulas earn their keep on sets of 3 to 10.
Is it safe to test my real one rep max?+
It can be, with a proper warm up, sound technique, a spotter or safety pins, and a base of training behind you. It is not something to attempt on a new lift, with a fresh injury, or alone under a loaded bar. An estimate from a set of 5 is usually enough to program with, which is the point of this tool.
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