How to Calculate Your One-Rep Max (1RM)
Your one-rep max (1RM) is the heaviest weight you can lift for a single clean rep. You don’t need to test it directly to know it: squat 100 kg for 5 solid reps and your estimated max comes out around 115 to 116 kg, depending on which formula you use. That’s the whole idea behind rep-max prediction, and it’s what the calculator below runs for you.
Why estimate instead of testing it directly
A true 1RM attempt is a maximal, near-failure lift. It takes a full warm-up, several ramping sets, and ideally a spotter, and it still carries some injury risk if your form breaks down under the heaviest load you’ve ever handled. Most lifters don’t need to touch that risk every few weeks just to track progress.
Rep-max formulas sidestep the problem. They take a set you already completed, comfortably below your max, and extrapolate what your true 1RM would be. You get a usable number for programming without ever grinding through an all-out attempt.
The three formulas
No single formula nails everyone’s max, so most calculators run several and average them. Here are the three behind the tool on this page.
Epley
1RM = weight x (1 + reps / 30)The most widely used formula. Simple, linear, and a good match for lower rep ranges.
Brzycki
1RM = weight x 36 / (37 - reps)Built around the idea that a set to failure at a given rep count corresponds to a fixed percentage of your true max. It’s the formula behind most percentage-based training tables, including the one further down this page.
Lombardi
1RM = weight x reps^0.1An exponential formula that sits between the other two at moderate rep ranges, and holds up a little better than Epley or Brzycki once reps climb past 10 or so.
Worked example: 100 kg for 5 reps
Say you squatted 100 kg for 5 clean reps. Here’s what each formula predicts:
| Formula | Calculation | Estimated 1RM |
|---|---|---|
| Epley | 100 x (1 + 5 / 30) | 116.7 kg |
| Brzycki | 100 x 36 / (37 - 5) | 112.5 kg |
| Lombardi | 100 x 5^0.1 | 117.5 kg |
| Average | (116.7 + 112.5 + 117.5) / 3 | 115.5 kg |
Averaging the three keeps any single formula’s bias from skewing your number. That average, roughly 115.5 kg, is what you’d use to set training percentages, not any one formula in isolation.
Why the formulas spread apart at higher reps
The gap between formulas is small at low reps and grows fast at high reps. Same 100 kg weight, different rep counts:
| Reps | Epley | Brzycki | Lombardi |
|---|---|---|---|
| 5 | 116.7 kg | 112.5 kg | 117.5 kg |
| 8 | 126.7 kg | 124.1 kg | 123.3 kg |
| 12 | 140.0 kg | 144.0 kg | 128.2 kg |
At 5 reps, the three estimates sit within 5 kg of each other. At 12 reps, Brzycki and Lombardi are almost 16 kg apart. This is the main reason 1RM calculators are most trustworthy at low rep counts: a set of 3 to 5 near failure gives a sharp, consistent prediction, while a set of 15 asks the formulas to extrapolate much further than they were designed for.
Building a percentage table for training
Once you have a 1RM estimate, the useful next step is turning it into a table of loads for different rep targets. Using the Brzycki relationship in reverse, from a 115.5 kg estimated max:
| Reps | % of 1RM | Weight |
|---|---|---|
| 1 | 100% | 115.5 kg |
| 3 | 94% | 109 kg |
| 5 | 89% | 103 kg |
| 8 | 81% | 93 kg |
| 10 | 75% | 87 kg |
| 12 | 69% | 80 kg |
This is exactly how a strength coach programs a block: pick a percentage range for the week’s goal (heavy triples at 90%+, volume work at 70-75%), then read the actual weight straight off the table instead of doing the math on the fly at the rack.
Calculate with your own numbers
Enter the weight you lifted and how many reps you completed. You’ll get the Epley, Brzycki and Lombardi estimates, an averaged headline number, and a full percentage table from 1 to 10 reps.
Common mistakes and limitations
Using a set that’s too far from failure. If you had 5 more reps left in the tank, the formulas overestimate, because they assume the set was taken close to muscular failure. A set that stops well short of failure understates your true effort and inflates the prediction.
Testing at high rep counts. As the table above shows, formulas diverge sharply past 10 reps. A set of 15 or 20 gives a much less reliable estimate than a set of 3 to 5, because endurance and pacing start to matter as much as raw strength.
Treating the estimate as a target for today. Your estimated 1RM is a theoretical ceiling assuming you’re rested, warmed up, and lifting with good form, ideally with a spotter. It is not something to attempt cold in the same session as your work sets.
Ignoring technique breakdown. A rep with poor form, even if completed, isn’t the same rep the formula assumes. If your last rep was a grinder with a form breakdown, your real capacity is closer to what the second-to-last rep suggests.
Skipping the warm-up before a real max attempt. If you do eventually work up to a true 1RM test, build to it gradually with ramping sets. Jumping straight from your estimated number to the bar with no warm-up is how good estimates turn into bad injuries.
Frequently asked questions
Which 1RM formula is most accurate? None of them is exact, and they diverge as rep count rises. Epley and Brzycki track closely at low reps and are the two most commonly used; Lombardi holds up a little better once reps climb into double digits. Averaging all three, as this calculator does, is a reasonable way to avoid betting everything on one formula’s blind spot.
How many reps should I use for the best estimate? Fewer is better. Estimates are most reliable at 10 reps or under, and a set of 3 to 5 taken close to failure gives the sharpest prediction. Past 10 reps, endurance and technique start to outweigh raw strength in determining how many reps you can grind out, so the formulas’ assumptions break down.
Is it safe to attempt my estimated 1RM? Treat it as a ceiling, not a plan for today’s session. It assumes a fresh, fully warmed-up lifter with solid technique and, ideally, a spotter. If you want to test a true max, work up to it gradually across several ramping sets rather than jumping straight to the estimated number.
Do I need different formulas for different lifts? No. Epley, Brzycki and Lombardi were derived from general strength data and are applied the same way regardless of the exercise, whether it’s a squat, bench press, or deadlift. What does vary by lift is how reliable the estimate feels in practice: compound lifts with a strong mind-muscle groove, like the deadlift, tend to match real testing more closely than lifts where technique degrades faster under fatigue.
Can I use this to plan an entire training block? Yes. Once you have an estimated 1RM, the percentage table turns it into concrete numbers for any rep scheme your program calls for, heavy triples, moderate sets of 5, or higher-volume sets of 8 to 10, without recalculating from scratch every session. Just re-test every few weeks as your strength changes, since the table is only as good as the 1RM it’s built from.