Most of the people reading this article have seen charts or looked at websites that predict how much weight they can lift. For example, the chart might say that if you can lift 200 pounds for 8 reps, then you should be able to do 250 pounds for one rep. These types of tools are useful, but they're also limited in practicality, because they aren't customized to the individual using them. They're okay for generalizations, but you need specific information tailored to fit you. That's where I come in.
The charts you've seen are called conversion charts, and they're based on the idea that if you can lift a certain weight for a certain number of reps, then you should be able to lift a certain amount of additional weight. Most of you probably have a version of a conversion chart in your head.
If a person says they can bench press 200 pounds for an 8 rep max, what do you think the probability is that the same person can do 210 pounds for one rep? Hopefully you answered "very high" because if you can do 200 for 8, then you can do 210 for one. What do you think are the chances of that same person benching 400? Practically nil. The strength required to bench 400 pounds is much greater than what is required to do 200 for 8.
This idea translates into the fact that every rep you perform, beyond the first rep, is worth a certain number of additional pounds. This is written as pounds per rep. If you can incline press 150 pounds for 10 reps, and you knew for sure that every rep at that weight was worth an extra 5 pounds, you can now figure out what your max single would be. The procedure to do so is outlined below:
- Reps performed = 10
- - Reps desired - 1
- Extra Reps = 9
- Pounds Per Rep x 5
- Extra Pounds = 45 pounds
- Original Weight + 150 pounds
- New Weight = 195 pounds
So using that basic formula, we estimate that this person can do a max single on the incline with 195 pounds. We got this because doing 150x10 basically meant the person had 45 extra pounds in the tank, so they could lift 45 pounds over the 150 pounds they were already lifting.
Now, in the above problem we needed to know the pounds per rep and I just gave it to you because I said it was 5 pounds per rep. When you look on a chart it's doing the same thing, it's telling you what value each rep has. But there are some problems with the generic charts.
Muscle Fiber Type
The charts don't take into account whether you're fast twitch or slow twitch dominant. That will significantly affect your conversion factor.
Men have a higher conversion factor than women, so each additional rep a man does is worth more weight. This means that women will be better at doing reps but guys will be better at going heavy, everything else being equal. For example, if a man and a woman can both leg press a maximum of 180 pounds for 10 reps, I would predict that the man will still have a higher single rep max even though the chart says they will be the same. This is also why when you take just a little bit of weight off the bar for a woman they often get a good number of reps with it.
Also known as "skill level." The more skilled you are at the exercise, the more each rep is worth.
The Exercise Itself
Something worth noting is that the conversion chart is exercise-specific. If you can barbell curl 100 pounds for ten reps, that will give you a certain one rep max. It doesn't follow that if you can also bench or squat 100 for 10, then your one rep max will be the same thing.
Muscle Group Size
Larger muscle groups have a higher conversion factor. When you add just five pounds on triceps kickbacks or lateral raises, you really feel the difference because only smaller muscles are working. So a small change in weight will significantly affect how many reps you can do. When you add five pounds to a lat pulldown or a deadlift it doesn't have the same effect.
Number of Reps
Most conversion charts acknowledge that the more reps you do, the less accurate any prediction is for a single rep max. Most charts go up to 12 reps but if you want to estimate your one rep max, using a set of 3 or 5 is a better idea. Anything above 12 enters in a lot of error. This is because each rep isn't weighted equally, even though most charts have it set that up that way. It takes more strength to go from doing one rep to getting a second rep with heavy weight than it does to go from doing 11 reps and then getting that 12th rep with a certain weight.
Now let's see how easy it is to create a conversion chart custom-tailored for you. All we need to know are two max sets for the same exercise, with a different number of reps in each set. Preferably 12 reps or fewer. You can do these two sets on the same day, or you can do them spread out over a few days, but don't wait too long or it won't be as accurate. If you do them on the same day, you want to be as fresh as possible for each set, so rest 5 to 10 minutes in between each set.
To use this method, first warm up as usual for your exercise of choice. Next, pick a weight you think you can do for 6-10 reps and try to perform as many reps with that weight as you can. Go to positive failure, meaning that if you did another rep you would definitely fail. If you do fail on a rep and require a spot, don't count that rep since you didn't complete it yourself.
Let's see how it works. Imagine you're a male lifter who wants to predict your single max weight on the bench press. For your first set, you lift 245 for a max of 10 reps. Next, rest a good long time, maybe five minutes or more, until you're no longer fatigued. (If you just can't recover from that first set, you'd do your second test set on another day.)
Next, select a weight you think you can do for 1-5 reps, or go up 20-75 pounds (the more weight you're lifting, the more weight you should increase). Let's say you choose 275, and you're able to do 6 reps with it. With that information, we can now figure out what your conversion chart is on the bench press. Here's how you do it:
Reps performed in set 1, minus reps performed in set 2, equals difference in reps
Example: 10 - 6 = 4 reps difference
Weight lifted in set 2, minus weight lifted in set 1 equals difference in weight
Example: 275 - 245 = 30 pound weight difference
Weight difference divided by rep difference equals pounds per rep
Example: 30 pounds / 4 reps = 7.5 pounds per rep
From our example, we see that you have a conversion factor of 7.5 pounds per rep in the bench press. Every rep you do is worth an extra 7.5 pounds. It's important to note that this is valuable not only for estimating your one rep max, but also for selecting the appropriate weight for almost any number of reps. For example, your conversion spread would look like this:
The following week, if you wanted to do a tough set of 8 on the bench, you should choose 260. If you wanted to go for a heavy set of 2, then 305 would be a good guess. There is still some room for error in this formula, but the point is that figuring out your very own personalized chart will be more accurate than using an online chart designed for the lifting public at large. And once again, this is only your conversion factor on the bench press. It doesn't apply to skull crushers, lat pulldowns, or deadlifts. If you were interested in those numbers, you would need to do the same process with those exercises.
Listed below are some example sets with the conversion factors figured out so you can see how I've done it.
- Set 1: 400 x 8
- Set 2: 455 x 3
- 8 reps - 3 reps = 5 rep difference
- 455 - 400 = 55 pound difference
- 55 / 5 = 11 pounds per rep on the deadlift
- Set 1: 315 x 12
- Set 2: 395 x 1
- 12 reps - 1 rep = 11 rep difference
- 395 - 315 = 80 pound difference
- 80 / 11 = 7.27 pounds per rep on the squat
- Set 1: 100 x 10
- Set 2: 115 x 5
- 10 reps - 5 reps = 5 rep difference
- 115 - 100 = 15 pound difference
- 15 / 5 = 3 pounds per rep on the barbell curl
- Set 1: 625 x 1 (raw)
- Set 2: 405 x 14 (raw)
- 14 - 1 = 13 reps difference
- 625 - 405 = 220 pound difference
- 220 / 13 = 16.9 pounds per rep on the bench press
(taken from Brian Siders's lifts at Kings of the Bench)
Do you hate math? Then the following table may be helpful for predicting your pounds-per-rep conversion factor based on your max lift poundage, without actually doing the calculations.
|Weight Lifted||Pounds Per Rep|
|Under 25 pounds||2|
|26 - 50 pounds||2.5|
|51 - 100 pounds||3|
|101 - 150 pounds||4|
|151 - 200 pounds||5|
|201 - 250 pounds||6|
|251 - 300 pounds||7|
|301 - 350 pounds||8|
|351 - 400 pounds||9|
|401 - 450 pounds||10|
|451 - 500 pounds||11|
|501 - 550 pounds||12|
|551 - 600 pounds||13|
|601 - 650 pounds||14|
|651 - 700 pounds||15|
Remember, though that this quick-and-dirty chart is just a rough guideline. If you want it to be more accurate, you'll have to do the tests on yourself and do your own conversion chart. Knowing your conversion chart can be very useful when trying to select your weight for your sets. It also makes it clear why you fight and claw for that extra rep. When you go from benching 250 for 5 to 250 for 7, you'll know that your one-rep max just went up. This information can also be useful if you work with other people, because sometimes selecting weights for someone whose strength level is different from yours can be a challenge.
I've tried to be as clear as possible when explaining this, but if you're having a hard time setting up a conversion chart for yourself, post your sets in the article discussions section and I'll try to talk you through the process. You'll need to tell me the exercise, the poundage, and the number of reps you did for each of the two sets. Remember, also, to do them with the same form.