Dumbbells to Barbells Conversion

Factual Questions
1

My brother and I use dumbbells almost exclusively when doing our chest workouts. We like that we get a longer range of motion and that, if we fail, we don’t drop a heavy barbell on our chests.

We were both off last night, we decided to go to the gym and do a max on bench. We both got less than we expected (I’m not complaining that I “only” got 305, I just thought I could have gotten 315).

Since one can lift more total weight when using a barbell than they can when using separate dumbells, this got me wondering if there was some kind of conversion system. For example, if I’m doing bench presses with 100 lb dumbbells, what is that equivalent to if I were doing barbell bench presses?

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2

I can’t find any studies on the topic, and even if they’re out there, I sincerely doubt that any of them would give a low-error model. There’s going to be a lot of variation here, particularly with something like the bench press.

3

One thing that might contribute to this is difference in the “quality” of the weights. At my gym I’ve noticed that the dumbells are usually dead-on with the weight listed on them (a dumbell marked 50 pounds actually weighs 50 pounds on the scale). However, some of the 45 pound plates that you use on the barbells are a bit variable in weight. Some of the plates marked 45 pounds are actually between 45 and 50 pounds (I haven’t seen them less than 45 pounds). Maybe it’s just cheap plates at my gym, but maybe it’s a “global conspiracy” to screw with weight-lifting math.

4

I suspect it’s the scale that’s in error, not the weights.
It’s relatively easy and cheap to manufacture the weight to a fixed, ummm weight.

5

I figured as much. Thanks for looking anyway.

6

I’ve always assumed that it would be the dumbbells that would have the variations in weight. My gym has some really old plate dumbbells (as opposed to the ones that are just big pieces of solid steel). If each plate is marked as 2.5, 5, or 10, then the bar itself must weight something, right? Therefore it would actually be a bit heavier than what it says it is.

7

If you only bench press with barbells, and don’t touch dumbells much, expect a big drop off. The drop off from jumping from barbell to dumbells is much less significant if you train both ways.

The conversion is unique to every individual, because the total weight you can lift with dumbells is greatly impacted by the role of the secondary supporting muscles. It all depends on the stregth/coordination of those secondary musles that stabilize and support the dumbells’ weight. Since a great number of other exercises impact those seconday muscles involved in the rep, it really comes down to case by case.

8

I’ve generally seen 5 lb. handles.

No big deal. Don’t forget, too, that anything I found on the bench press would only be applicable to the bench press.

9

Um, you are counting the weight of the bar, aren’t you?

10

If I go heavy; i.e. use about as much weight as I can handle for 5 or 6 reps, I find that if I use dumbells on a mild incline, I can use about 68% the total weight I use on a seated chest press machine. I haven’t tried a standard barbell in a log time, but my “heavy” weight for that would have to be somewhere in between.