I believe they're well aware of their own power. I think the idea of them being able to sense or feel their own power would be similar. Raditz is a weakling, but even he says he's going to "increase the power" in his attacks. That would at least imply he knows his own power.
For example, Goku sensed the drastic drop in power Super Boo had and was able to compare that to his full-power in Super Saiyan 3. I don't think Goku would need to sense his Super Saiyan 3 Chi to know he'd get his ass whooped in that situation, if that makes sense.