If you Google your original question (what I just did) you'll find people who, e.g., weigh 80 kg and when they put a scale under their hands and do pushups, the reading is 55 to 60 kg, depending on where they are in the pushup.
If you raise your feet some, you'll get closer to your bodyweight but by the time you'd get to bodyweight, you'd be doing an upside down military press and not a pushup/bench movement.
Try working pushups, controlled and at a moderate speed, not quick, in sets of 8 for a few sets. Then to work up to the same with your feet raised so that, at the top of the pushup, your body is parallel to the ground. If you can do a few sets of 8 of those, I'd say you'd be able to do a bodyweight bench press with very little training.
The other thing someone has to say here is that a bodyweight bench press is nothing to write home about. Most standards I see suggest 1-1/4 or 1-1/2 times bodyweight for a single, or perhaps 15 reps @ bodyweight as being at least not weak, but that's still not exactly strong bench pressing, either. I've done more than 1-1/4 times bodyweight and I'm an _awful_ bench presser.
-S-