One Rep Max Calculator
Enter any set you have actually done and get your estimated one rep max, the formula behind it, and how much to trust it.
An estimate from a submaximal set, not a tested max. The further your set is from a true single, the wider the error, which is what the confidence rating is telling you. Warm up properly and use a spotter before testing anything near this number.
Example: 100 kg lifted for 5 reps is an estimated one rep max of about 116.7 kg with the Epley formula.
How this is worked out
A one rep max is the heaviest weight you can lift once with good form. Almost nobody tests it often, because a true max is taxing to recover from and risky to attempt alone, so it gets estimated from a set you already did.
Up to ten reps this calculator uses the Epley formula, which is the best validated in that range. From eleven reps it switches to Mayhew, an exponential model that keeps returning sensible numbers where the linear formulas start inflating. This is the same rule the Workout With Me app applies when it detects a personal record.
The confidence rating matters more than the number. A set of three tells you a lot about your max. A set of twenty five tells you about your work capacity and only guesses at your max, so the calculator says so instead of reporting both with the same false precision.
Epley: 1RM = weight x (1 + reps / 30) Mayhew: 1RM = 100 x weight / (52.2 + 41.9 x e^(-0.055 x reps))
What a one rep max is actually for
On its own the number is trivia. What makes it useful is that nearly every written training program is expressed as a percentage of it. A program that says five sets of three at 85 percent is meaningless until you have a max to take 85 percent of.
It is also the cleanest way to see whether you are getting stronger. Total weight moved goes up when you add sets, and how a session felt drifts with sleep and stress. An estimated max from your top set of the day is one number that only moves when your actual strength does.
You do not need it to be exact. You need it to be consistent, computed the same way every time, so that the trend across months is real even if any single estimate is a few kilos out.
Epley, Brzycki, Mayhew and Lombardi compared
There are dozens of one rep max formulas and they were all fitted to different groups of lifters doing different exercises. They agree within a couple of kilos on a heavy triple and drift apart badly once the reps climb.
Brzycki is the one most other calculators use, and it is fine up to about ten reps. Past that its denominator shrinks toward zero and the estimate runs away, until at thirty seven reps it stops producing a number at all. Lombardi flattens too early and understates high rep sets. Mayhew was built for exactly this range, which is why it takes over here.
| Reps | Epley | Brzycki | Mayhew | Lombardi |
|---|---|---|---|---|
| 1 | 103.3 kg (228 lb) | 100 kg (221 lb) | 108.9 kg (240 lb) | 100 kg (221 lb) |
| 2 | 106.7 kg (235 lb) | 102.9 kg (227 lb) | 111.4 kg (246 lb) | 107.2 kg (236 lb) |
| 3 | 110 kg (243 lb) | 105.9 kg (234 lb) | 114 kg (251 lb) | 111.6 kg (246 lb) |
| 4 | 113.3 kg (250 lb) | 109.1 kg (241 lb) | 116.5 kg (257 lb) | 114.9 kg (253 lb) |
| 5 | 116.7 kg (257 lb) | 112.5 kg (248 lb) | 119 kg (262 lb) | 117.5 kg (259 lb) |
| 6 | 120 kg (265 lb) | 116.1 kg (256 lb) | 121.5 kg (268 lb) | 119.6 kg (264 lb) |
| 8 | 126.7 kg (279 lb) | 124.1 kg (274 lb) | 126.3 kg (278 lb) | 123.1 kg (271 lb) |
| 10 | 133.3 kg (294 lb) | 133.3 kg (294 lb) | 130.9 kg (289 lb) | 125.9 kg (278 lb) |
| 12 | 140 kg (309 lb) | 144 kg (318 lb) | 135.4 kg (299 lb) | 128.2 kg (283 lb) |
| 15 | 150 kg (331 lb) | 163.6 kg (361 lb) | 141.7 kg (312 lb) | 131.1 kg (289 lb) |
| 20 | 166.7 kg (368 lb) | 211.8 kg (467 lb) | 151.2 kg (333 lb) | 134.9 kg (297 lb) |
All four formulas applied to the same 100 kg set. They agree closely at low reps and separate badly above ten, which is why the calculator above switches from Epley to Mayhew at eleven rather than pushing one formula past the range it was fitted for. Brzycki is left blank where it breaks down entirely.
Training load chart: what to lift at each percentage
Once you have a max, this is the table you actually use. It converts the percentages a program prescribes into weight on the bar, and tells you roughly how many reps that load should be good for.
The rep column comes from the RPE table used across strength coaching, read at RPE 8, meaning a set you finish with about two reps left. If a prescribed percentage is costing you noticeably more reps than the table says, your max estimate has drifted and it is worth re-checking with a fresh top set.
| % of 1RM | Weight | Reps at this load |
|---|---|---|
| 100% | 100 kg (221 lb) | 1 |
| 95% | 95 kg (209 lb) | 1 |
| 90% | 90 kg (198 lb) | 1 |
| 85% | 85 kg (187 lb) | 3 |
| 80% | 80 kg (176 lb) | 4 |
| 75% | 75 kg (165 lb) | 6 |
| 70% | 70 kg (154 lb) | 8 |
| 65% | 65 kg (143 lb) | 10 |
| 60% | 60 kg (132 lb) | 12 |
Percentages of a 100 kg one rep max. The rep column is read off the RPE 8 row of the Tuchscherer table, so it is the work you could do on a hard but not maximal set, which is where a written program actually sits.
One rep max chart by weight and reps
The quick lookup, if you would rather not type. Find the weight you lifted down the left, the reps you managed across the top, and read off the estimate.
| Weight lifted | 3 reps | 5 reps | 8 reps | 10 reps | 12 reps |
|---|---|---|---|---|---|
| 40 kg (88 lb) | 44 kg (97 lb) | 46.7 kg (103 lb) | 50.7 kg (112 lb) | 53.3 kg (118 lb) | 54.2 kg (120 lb) |
| 60 kg (132 lb) | 66 kg (146 lb) | 70 kg (154 lb) | 76 kg (168 lb) | 80 kg (176 lb) | 81.2 kg (179 lb) |
| 80 kg (176 lb) | 88 kg (194 lb) | 93.3 kg (206 lb) | 101.3 kg (223 lb) | 106.7 kg (235 lb) | 108.3 kg (239 lb) |
| 100 kg (221 lb) | 110 kg (243 lb) | 116.7 kg (257 lb) | 126.7 kg (279 lb) | 133.3 kg (294 lb) | 135.4 kg (299 lb) |
| 120 kg (265 lb) | 132 kg (291 lb) | 140 kg (309 lb) | 152 kg (335 lb) | 160 kg (353 lb) | 162.5 kg (358 lb) |
| 140 kg (309 lb) | 154 kg (340 lb) | 163.3 kg (360 lb) | 177.3 kg (391 lb) | 186.7 kg (412 lb) | 189.6 kg (418 lb) |
| 160 kg (353 lb) | 176 kg (388 lb) | 186.7 kg (412 lb) | 202.7 kg (447 lb) | 213.3 kg (470 lb) | 216.6 kg (478 lb) |
Estimated one rep max for common working sets, using Epley up to ten reps and Mayhew above it. Find the weight you lifted, then the reps you got.
How often to re-estimate
As a beginner, every few weeks, because you are genuinely getting stronger that fast. Once progress slows to monthly, checking monthly is enough, and checking more often mostly measures how well you slept.
Take the estimate from a real top set rather than an all out grinder. A set taken to failure is not more informative here, it is just harder to recover from, and it costs you the next session for a number you could have had for free.
Turning the number into a program
The point of a max is deciding what to lift next week. That means picking a percentage, holding it for a block, adding weight when the reps come easily, and backing off before you stall rather than after.
Doing that by hand across six muscle groups and a dozen exercises is where most people quit. Workout With Me keeps an estimated max per exercise, updates it every time you log a set, and writes the next session's weights against it.
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Key Takeaways
- A one rep max is the heaviest weight you can lift once, and almost everybody estimates it rather than testing it.
- This calculator uses Epley up to ten reps and Mayhew from eleven, which is the same rule the Workout With Me app uses.
- The confidence rating is the honest part. A set of twenty produces a number, but a much less reliable one than a set of three.
- The main use of a max is converting the percentages a program prescribes into weight on the bar.
- Re-estimate every few weeks as a beginner and roughly monthly once progress slows.
- Use a real top set rather than a set to failure. Failure costs you recovery without improving the estimate.
What is a One Rep Max?
Your one rep max, or 1RM, is the heaviest weight you can lift for a single repetition with correct form. Because testing it is taxing and risky, it is usually estimated from a lighter set taken close to failure, using a formula that relates weight and reps to a predicted single.
A gym buddy whose one rep max is within about 15 percent of yours — roughly one plate — can share a loaded bar and spot you safely, which is the window a strength compatibility score is built around.
RPE and percentage of max describe the same set from opposite ends: five reps at RPE 8 is about 79 percent of your one rep max, so either number can set the day's working weight.
Frequently Asked Questions
How do I calculate my one rep max?
Take a set you completed with good form, enter the weight and the number of reps, and apply a formula that relates the two. Epley, weight multiplied by one plus reps divided by thirty, is the most widely validated up to ten reps. Above ten reps Mayhew gives a more sensible answer because it does not keep climbing in a straight line.
Which one rep max formula is the most accurate?
It depends on the rep range. Up to about ten reps Epley and Brzycki agree closely and both are well supported. Above ten, the linear formulas overshoot and Mayhew's exponential model holds up better. No formula is accurate for everyone, because the relationship between reps and a true max varies with training history and with the lift itself.
Is it safe to test my actual one rep max?
It can be, with a full warm up, a spotter or safety bars, and a training base behind you. It is also unnecessary for most people. A heavy triple gives you an estimate within a few percent, costs far less recovery, and does not put you under a bar you might not finish.
Why is my one rep max different on this calculator?
Most calculators use Brzycki for every rep count. This one follows the rule the Workout With Me app uses, which switches to Mayhew above ten reps because Brzycki inflates badly there. On a set of five the two agree within a few kilos. On a set of eighteen they will not, and the comparison table on this page shows exactly how far apart they get.
Does a one rep max transfer between exercises?
No. A max is specific to the lift, and often to the bar and setup. A leg press max tells you very little about your squat, because the machine supports your torso and takes stabilisers out of the equation. Estimate each lift you care about separately.