Anyone who spends any significant time “under the bar” is going to eventually want to know what their 1 rep max is. The problem is that you’re likely not hitting the gym to go for a new max anytime soon, nor should you even attempt a new max that often. If you know how to calculate your one rep max, this might not be an issue. The problem is that not many know the proper formula. Lucky for you, we have a one rep max calculator below to make it easy.
All you have to do is enter the weight you used into the max rep calculator below, then select how many reps you did. You’ll then be given:
You might be wondering how this 1 rep max calculator works. If you were interested in calculating one rep max, you’d first want to reference the below chart, as it compares rep maxes to percentages. In other words, if you can do X reps, then that corresponds to Y% of your 1RM:
If you did 3 reps with a weight before failing, then that was obviously your 3RM (three rep max), and your 3RM equates to 93% of your 1RM. You’d then divide the weight you lifted by the percentage to find your 1RM.
So say you benched 230lbs for 10 reps, wanted to know what your estimated one rep max was, but didn’t have our max rep calculator handy. You could save the details on the one rep max calculator chart above, and find 10RM since that’s how many reps you performed. 10RM = 75%, so divide 230lbs by .75 and round to the nearest 5lbs increment.
230/.75 = 306.7 which rounds to 305
Using this 1 rep max calculator formula, your estimated bench press 1RM would be 305lbs.
On the flip side, if you wanted to calculate a particular RM, and knew your one rep max, you could just apply the percentages above to it. So if you knew your deadlift 1RM was 260lbs, and needed to know what your corresponding 8RM would be, you’d look above at the one rep max calculator chart. You’d see that 8RM = 80%, then multiply and round accordingly:
260 x .8 = 208 which rounds to 210
Based on a 1RM of 260lbs, your deadlift 8RM would be roughly 210lbs.
It bears mentioning that anything figured from this one rep max calculator, while as accurate as possible, should still be considered an estimate. There can be variances due to rounding weights to the nearest increment, and from person to person since not everyone responds to rep ranges the same exact way.
In addition, remember that all calculations only ever apply to a single exercise. You can’t input bench press numbers, expecting the formula to work for your incline press. Back squat poundages won’t apply to your front squat, and so on.
It can be tempting to work up to and test your 1RM often, but you really don’t need to do it any more than once every 3-4 months. Doing it more than that can be hard on the joints, leave you susceptible to injury, and be quite draining on the central nervous system.
Having said this, some people might like to bring up Louie Simmons, who has his lifters at Westside Barbell building up to a 1RM in a bench press and squat variation every single week. Louie’s system is different in that he rotates exercise variations every 3 weeks, meaning his guys aren’t always maxing out on the same lifts. At the same time, this is only part of his system and his lifters are among the best in the world. What applies to them won’t apply to you and they’re the exception to the rule.
Besides, while competitive powerlifters need to keep a close eye on their 1RMs for obvious reasons, bodybuilders, athletes, and regular gym goers need to be getting stronger across the board. This is where a one rep max calculator can come in handy. Not only can you figure your estimated 1RM without having to put 1RM stress on your body, but using the chart above, you can also compare rep ranges as you progress.
Say this week you deadlift 275lbs for 6 reps, then two weeks later deadlift 315lbs for 3 reps. While that’s a significant jump in weight, you’ve also cut your reps in half. Using a one rep max calculator can normalize those two sets of data. This will help you gauge your progress and ensure you’re getting stronger overall instead of in just one particular rep range.
When the day comes that you want to actually test your 1RM instead of relying on a max rep calculator, then be sure to put safety first. Have a spotter with you if possible. If you can’t, then bench or squat inside of a cage style power rack where you can bail out on a lift when you hit failure.
Do a couple easy warm up sets, followed by progressively heavier singles. There are no “right” or “wrong” ways to do this, as it will depend on how much weight you’re building up to. You’ll want to do enough sets to adequately prepare you and warm you up for your max attempt(s), but not so much that you’re overly fatigued when you hit the top end.
If you knew your max was around 230lbs, then an example buildup might look as follows:
Take 2-3 minutes rest between sets to recover completely and let your CNS be ready for your next set. You’ll see that jumps in weight were bigger earlier on, but then decreased to a minimum once you got near and beyond your estimated max.
Instead say your estimated max was around 425lbs. An example buildup might look like:
This time, because you were building up to a much heavier weight, your jumps had to be bigger and you’d do more buildup sets.
A one rep max calculator isn’t going to always be perfect, but it’s pretty close. It can give you a good estimation of how your strength is progressing without having to put excess wear and tear on your body. In addition, percentage charts give you something to compare to when weights are going up, but reps going down. Use these tools to keep accurate records, and you’ll be in a much better position to gauge and analyze your strength progress.