Strength Tools
One Rep Max
Calculator
Enter a set you have actually done. You get an estimated one rep max from six published formulas, the training percentages underneath it, and an honest note about which of those formulas you should be ignoring at your rep count.
Estimate your max
Estimated 1RM
260lb
Average of valid formulas
Training max (90%)
235lb
Program off this, not the estimate.
All six formulas
| Formula | 1RM (lb) | In range |
|---|---|---|
| Epley | 265 | Yes |
| Brzycki | 255 | Yes |
| Lombardi | 265 | Yes |
| Mayhew et al. | 270 | Yes |
| O'Conner et al. | 255 | Yes |
| Wathan | 260 | Yes |
Warm-up to your top set
105
× 5 · 40%
145
× 5 · 55%
180
× 3 · 70%
220
× 2 · 85%
Load for every rep target
| Reps | % of 1RM | Load (lb) |
|---|---|---|
| 1 | 100% | 260 |
| 2 | 95% | 245 |
| 3 | 93% | 240 |
| 4 | 90% | 235 |
| 5 | 87% | 225 |
| 6 | 85% | 220 |
| 7 | 83% | 215 |
| 8 | 80% | 210 |
| 9 | 77% | 200 |
| 10 | 75% | 195 |
| 11 | 72% | 190 |
| 12 | 70% | 180 |
What a one rep max actually is
Your one rep max is the heaviest weight you can move for a single clean rep of a given lift. It is the reference number nearly every strength program is written against — when a plan says “3 sets of 5 at 80%”, 80% of your 1RM is the load it means.
Almost nobody needs to actually test one. Testing costs a session, takes days to recover from, and carries real risk if you are tired or your technique is having an off day. A hard set of five run through a rep-max formula gets you close enough to program from, for free, off a set you were going to do anyway.
How this calculator works
And where it differsYou did a set. The calculator takes that weight and rep count and runs six published rep-max equations against it — Epley, Brzycki, Lombardi, Mayhew, O’Conner and Wathan — then averages the ones that are still inside the rep range they were actually validated on.
That last part matters and most calculators skip it. Brzycki is excellent at five reps and nonsense at twenty, because its denominator collapses as reps climb toward 37. Quietly folding a broken number into an average makes the average worse. Here, a formula that has left its validated range gets flagged and dropped from the average rather than silently dragging it.
One more thing we do differently: if you enter a single rep, every formula returns exactly the weight you lifted. Several of these equations technically read above the input at one rep — Epley says a 100kg single implies a 103kg max — which is an artifact of fitting a curve, not a result. A single is a max. We return it as one.
The six formulas
w = weight, r = reps| Formula | Equation | Good to |
|---|---|---|
| Epley | w × (1 + r / 30)The most widely used one. Runs slightly high on long sets. | 10 reps |
| Brzycki | w × 36 / (37 − r)Agrees with Epley at 10 reps, reads lower below that. Falls apart past 12 — the denominator collapses. | 10 reps |
| Lombardi | w × r^0.10The most conservative of the set. A useful sanity floor. | 12 reps |
| Mayhew et al. | w / (0.522 + 0.419 × e^(−0.055r))Fitted on bench press sets to failure. Holds up better than most on long sets. | 15 reps |
| O'Conner et al. | w × (1 + 0.025r)Deliberately simple and deliberately cautious. Good for beginners. | 10 reps |
| Wathan | w / (0.488 + 0.538 × e^(−0.075r))Often the closest to a tested max in validation studies. | 15 reps |
The one people argue about: Epley and Brzycki return identical answers at exactly ten reps. Below ten, Brzycki reads lower. Above twelve, Brzycki stops being usable at all — its denominator is 37 minus your rep count, so it runs off toward infinity as sets get long. That is not a bug in the formula, it is the range it was fitted on.
How accurate is this?
For a set of three to six reps taken genuinely close to failure, expect the estimate to land within about 5% of a tested max. That is good enough to write a training block around and nowhere near good enough to argue about on the internet.
The accuracy killer is not the formula — it is reps in reserve. Every one of these equations assumes you stopped because you physically could not do another rep. If you racked a set of five with three still in the tank, the formula has no way to know that and will hand you a number that is badly low. Take the set close to failure or treat the output as a floor.
1–2 reps
You are basically testing a max already.
3–6 reps
The sweet spot. Tightest estimates, safe to repeat.
10+ reps
Fatigue and pacing take over. Treat as a rough guide.
What to do with the number
Program off a training max, not the estimate
Take 85–90% of the number and run your percentages off that. Your real max fluctuates with sleep, stress and training phase; a conservative anchor means a bad Tuesday still produces a usable session instead of three missed reps and a dented ego.
Re-estimate rather than re-test
Every few weeks, take one hard set of five on your main lift and run it through again. You get a trend line for the price of a set you were going to do anyway, and you never spend a session testing.
Watch the spread, not just the average
When the six formulas cluster tightly, your set was probably a clean, close-to-failure effort. When they fan out, you are either at a high rep count or you entered something the formulas disagree about. The spread is a confidence interval in disguise.
Strength is a means, not the point
If you are training for a hybrid event rather than a platform, the max is a dial you turn, not a score you chase. I use mine to set working loads for compound days and then get on with the running. It is one input.
If you want the percentages turned into an actual programme, the 5/3/1 calculator takes three maxes and builds the full four-week Wendler cycle off them — training max already applied.
Per-lift calculators
Each lift lies differentlyThe math is the same for every lift, but the ways an estimate goes wrong are not. Deadlifts read high because there is no eccentric and grip gives out early. Squats read whatever your depth says they read. Bench is the most trustworthy of the three, largely because that is what most of the research was done on.
Questions people actually ask
How accurate is a one rep max calculator?
For a set of three to six reps taken genuinely close to failure, expect the estimate to land within about 5% of a tested max. Accuracy falls off fast outside that: long sets, sets with reps left in the tank, and untrained lifters all widen the error. The formulas assume you stopped because you could not do another rep, so anything else is measuring the wrong thing.
Which 1RM formula is the most accurate?
None of them, consistently. Epley and Brzycki agree exactly at ten reps and diverge below it, Brzycki reading lower. Wathan and Mayhew tend to hold up better on longer sets. That is why this calculator defaults to averaging the formulas that are still inside their validated rep range instead of asking you to pick a winner — the spread between them tells you more than any single number.
What is the difference between Epley and Brzycki?
Epley is weight × (1 + reps/30) and Brzycki is weight × 36/(37 − reps). They cross at exactly ten reps and give identical answers there. Below ten reps Brzycki returns a lower, more conservative estimate. Above twelve reps Brzycki starts to break down because its denominator collapses toward zero, so it should not be used for long sets.
How many reps should I use for the most accurate estimate?
Three to six. Below that you are basically testing a max anyway, and above that fatigue, technique drift and pacing start to dominate. A hard set of five is the sweet spot for most lifters — close enough to a max to be predictive, far enough from one to be safe to repeat.
Should I test my one rep max instead of estimating it?
Most people do not need to. Testing costs a session, takes a few days to recover from, and carries real injury risk under fatigue or bad technique. If you compete in powerlifting or weightlifting you will test on the platform anyway. If you train for general strength, health or a hybrid event, an estimate from a hard set of five is accurate enough to program from and costs you nothing.
What is a training max and why is it lower than my 1RM?
A training max is a deliberately conservative number — usually 85–90% of your estimated max — that you run your working percentages off. The point is that your true max moves around with sleep, stress and where you are in a block. Programming off 90% means a bad week still produces a workable session instead of a missed one. Jim Wendler built 5/3/1 around this idea.
Does RPE change the estimate?
Enormously. These formulas assume RPE 9–10, meaning zero to one reps left in reserve. If you stopped a set of five with three reps still in the tank, the formula treats it as a maximal effort and hands you a number that is badly low. Either take the set close to failure or accept that the estimate is a floor, not a prediction.
Can I use this for dumbbells, machines or bodyweight movements?
For dumbbells and most machines, yes — enter the total load and treat the result as specific to that implement. For bodyweight movements like pull-ups and dips you need to add your bodyweight to the external load for the math to mean anything, and the result still will not transfer cleanly to a barbell lift.
The rest of the strength tools
All free, no sign-upWho is behind this calculator
I am not a supplement company with a blog. I am one person who trains, races HYROX, and publishes every session I do — 23 of them across 5 weeks, free, with no email gate. The strength numbers this calculator produces are the same ones I use to set my own working loads.
If something here is wrong, it is worth telling me about — the formulas are all published research and the implementation is open source.