Hey everyone I do the best I can to try and practice safe sex if the opportunity ever presents itself but I have yet to find a condom that fits. I have used them all, the regular size and the small size and every single one just slips right off even when I'm erect. I don't even need to stretch the condom out to slide my erect penis in. It just slips right in and then falls right off. Shouldn't a penis of 3.7 inches long erect and 0.7 inches wide erect and 0.4 inches thick with a measured circumference of 2.7 inches be able to use regular size condoms. I don't know what to do, please help. They all seem to be about 4 inches to long and way to big around.

Have you tried all the snugger fit ones? There's a fair few brands out there. Have a look here and see if anything catches your eye:

Snugger Fit Condoms

I order from the site myself; they're good to do business with and I think they answer questions by email. Also, there's the Female Condom, one or two of which you could keep on hand (although I'm only assuming you're planning on having sex with women- please accept my apologies if I'm wrong) as it stays inside her and doesn't need to be on you. They feel a little different, but they certainly work.
And good for you for wanting your sex to be safe!

Hope this helps.

You could try a cock ring, if you absolutely cannot get a condom to stay on.