I did the leg press yesterday. I had a 45lb and a 10lb on each side. Now, I dunno if I lifted 55 or 110. How can you determine that?

Sorry, but without knowing what type of machine it is, it's impossible to tell. Ask your gym.

Are you a pretty strong gal? I'm pressing 50kg right now, but I'm recovering from an injury...and don't want to stress myself. I don't find it hard. I'm pretty strong though. I believe I could press 110 by working up to it....not sure, but it wouldn't be easy. So if you're strong and you found it pretty tough, it's probably the 110.

I'm used to a leg press with just one set of weights. I've never seen one with two! So I suppose that would lead me to believe that if you have two sets and you are pressing 55lb with each leg, that it's cumulative 110lb...

The weight doesn't matter. What matters is good form and that you try to increase the weight over time.

Well, it matters if you're going to use a different leg press sometime and need to know how much weight to put on it.

OP, if it was the sled type where you add plates to each side and then move the whole platform with plates, you lifted 110 lb PLUS the weight of the sled. You'll need to ask someone at the gym what the weight of the sled is, then add that to your total. Or there may be a sticker somewhere on it with that information.

The fact that they are "different" means that you will have to experiment to determine what the similar weight is.

100lbs on one machine will be different than 100lbs on another.

Right, that's why I encouraged including the weight of the sled. That way you'll always know what your total is.