The Best Way To Calculate 1 Rep Max
Here's the short version of what I want to explore in this post: Rep max calculators aren't that useful.
The best 1 rep max calculator is your own experience. Each lifter is too individual so the online calculators aren't actually a very useful tool. Let me explain why.
When I was competing in weightlifting and peaking during a strength program, I hit a a 5RM at 345lbs and a 3RM at 365lbs in the back squat. A couple weeks later, after a peaking phase, I hit a 1RM of 380lbs. I missed 385lbs.
Most one-rep max calculators correlate your 3RM with 90%. I could actually do 96%.
Most one-rep calculators correlate your 5RM with 85%. I could actually do nearly 91%.
While most calculators would have been psyching me up for a 405lbs squat, that just wasn't going to happen. I can add 4-5% to my 3RM, not 10%.
The point is that your ability to perform reps at a percentage of your max is very individual. Some will fall well below or above what most tables recommend.
Case Study: How Coach Alastair Calculates 1 Rep Max Squat
Let's take another example of an elite powerlifter, Alastair MacNicol. He's a fellow coach at Quantum CrossFit (my Toronto-based gym) and the head of our powerlifting program. In training leading up to a meet, his squat numbers looked like this:
5RM: 562 (89% of gym max, 87% of comp max)
3RM: 595 (94% of gym max, 92% of comp max)
1RM (gym): 630
1RM (comp): 644
In the same period, his deadlift numbers looked like this:
5RM: 620 (85% of gym max and 81.5% of comp max)
3RM: 673 (92% of gym max and 88.5% of comp max)
1RM (gym): 727
1RM (comp): 760
His bench percentages were similar to deadlift.
He's a bit closer to most rep-max calulators than I am, but he doesn't match it exactly. If he were using these tables to pick his attempts in the gym, he could easily be off by 10's of pounds. It's also interesting to note the discrepancy between his squat and deadlift rep-max percentages. It goes to show that rep-max abilities differ by lift as well as by person.
FOR Reference: Common Repetition Max Tables
Brzycki, Matt (1998). A Practical Approach To Strength Training. McGraw-Hill.
Baechle TR, Earle RW, Wathen D (2000). Essentials of Strength Training and Conditioning, 2: 395-425.
dos Remedios R (2007) Men's Health Power Training, Rodale Inc. 23.
WHAT AFFECTS Your REP MAX ABILITY?
It turns out that your ability to do reps at submaximal loads is greatly influenced by (in no particular order):
- Gender: females tend to be able to do more reps at higher percentages than males.
- Training Age: Lifters who've been training consistently for longer periods of time (example: 6 years of structured weight training) tend to do less reps at a given percentage than relative beginners (1 year of training).
- Athletic Background: Clients with extensive endurance training tend to be significantly better a doing more reps at higher percentages than those without that training background.
- Exercise Selection: I've found that some clients are just better at doing reps on certain exercises than others. Perhaps this is linked to previous training experience, but I haven't found any strong correlation. Either way, understand that your rep percentages for squat, deadlift, cleans, presses, bench, chin-ups etc. will potentially all be different.
- Genetics/Inherent Characteristics: Some athletes are more explosive and less enduring than others, regardless of training. Some coaches call this "neuromuscular efficiency" or NME.
Testing For Neuromuscular Efficiency
Here's how NME works. A frequent test would be to build to a back squat 1RM, then after 10-mins of rest, to do as many reps as possible at 85%. Typically we'll use a  tempo to keep this standardized, since taking a 5sec rest at the top of each squat can change performance significantly.
If you get 1-3 reps, you're considered to have very high NME. If you have high NME, you can recruit more muscle fibers for each rep, so you fatigue faster. Although this doesn't always hold true, changes are you have good speed and a good vertical jump.
If you get 4-7 reps, you've got roughly average NME.
If you get 8+ reps, you've got low NME. If you have low NME, you recruit less muscle fibers for each rep, giving you an ability to endure and continue working.
Neither is good or bad. Some activities favour low NME individuals (general things that involve more endurance) and other sports favour high NME athletes.
In the context of a lifting program we can immediately see a problem.
If athlete A can do 3 reps at 85%, and athlete B can do 8 reps @ 85%, they'll have a completely different training effect from the same workout, for example: 4x4@85%
Athlete A won't be able to complete the first set. Athlete B will have a relatively moderate session. Coach's should have awareness of this when designing programs. Repetition ranges (i.e. do 4-6 reps) and Rate of Perceived Exhaustion (RPE... i.e. go to a weight that feels like you have 2 more left in the tank) are some methods of dealing with this. The other is working with an experienced coach who knows what each individual client is capable of.
I'm going to talk more about adjusting your training based on neuromuscular efficiency in another post. Stay tuned for that one, because there's a lot of confusion about it.
When Are Rep Max Calculators Useful?
I remember when I was a new lifter. Every time I hit a new rep PR, I'd punch it into the 1RM calculator and dream about what my new 1 rep max would be. But that never actually materialized into anything. It wasn't useful. It didn't guide my training. It just pumped me up in the moment.
The truth is that there are very few sports where accurately predicting your 1RM is essential. So the question is: why do you care what some chart says about your theoretical 1RM?
Even in the sport of powerlifting or weightlifting, 2nd and 3rd attempts are done largely by feel and experience vs. any kind of rep-max chart.
Rep max calculators give us some insight into the average. That's about it. Don't put too much stock in and just focus on gradual improvement according to your coach's training plan.
A Better Alternative to 1RM Calculators
The most accurate way to find your 1RM is to test it. Period. There's no substitute for that.
The problem is that there's not much value in testing a 1RM for a new lifter. Their beginner status means they're constantly improving and arguably not truly capable of demonstrating real limit strength.
For advanced lifters, you're only going to do a true test a few times a year based on how stressful it is and how much training needs to happen to stimulate adaptation and improvement.
Aside from actually testing, it takes experience to be able to estimate. Throw out the rep max calculators and tables. You've got to understand where you sit on the rep-max continuum to make a somewhat predictable guess. What's the typical relationship between a your 3RM and your 1RM in a given exercise? It's different for everyone, so you need to understand how it works for you.