I don't have any measurements, but just based on feel, it feels fine as far as bulk and size.
The Spigen Neo Hybrid makes it feel MUCH larger than naked. The Apple leather case is fine.
Only downside to the leather case is that since they left the bottom open, that edge rubs against your pinky if you tuck your pinky under the phone while using it.
The phone feels lighter with the case on than off, I suspect because it balances the phone better and distributes the weight more evenly.
Love the feel of the leather. It would be perfect if it covered the bottom like the 5S case. And if the price was lower.