Q: How do you convert the weights you can do with machines to free weights?
A: First, consider that getting stronger with free weights will make you stronger with machines, but it doesn’t necessarily work the other way.
One reason for the difference is that machines don’t require you to stabilize the weight—and don’t let Smith machines fool you, as the bar moves along rails. So whatever your max is on a machine, prepare to be disappointed when you try the same exercise with free weights.
Another issue is that many machines, especially Hammer Strength and MedX, give you advantageous leverage. For some exercises, it’s a 3-1 ratio, so that if you can lift 100 pounds with a free weight exercise, you might be able to use as much as 300 pounds with an equivalent machine exercise.
Finally, consider that barbells are more stable than dumbbells. For example, if you have good stabilizer muscles, you might be able to do as much as 90 percent of your best barbell bench press weight when performing semi-supinated dumbbell presses. Thus, if you bench press 200 pounds, you should be able to press a pair of 90-pound dumbbells.
The lesson here is that if your primary goal is to lift more weight in free weight exercises, keep your machine training to a minimum. Further, you should keep accurate records of how much you can lift on specific machines to see how they compare to free weight exercises and other machine exercises. This way, you don’t have to do as much experimenting with your weight selections when you switch from one form of resistance to another.