I would recommend not touching the beam. Even if you knew the "number" you'd also need to know the laser's "number", and, they are rarely accurately rated.
IE: Lets say you did a detailed study, and found for your skin, on the part you wanted to touch, the number was 5 mw....so you bought a 5 mw laser, and assumed you were fine, but, it was underrated and actually put out 50 mw, and, burned you.
If you are asking this question, essentially, just do your best to not touch it...that will be safer.
All of the "cheap" red pens that I buy are over 100mW. You are likely "safe" if it one of those cat toys that take button cell batteries. Don't just assume that if you get a green laser that you can barely see the beam in a dark room has a really low output either. I just received a green one last week that was very dim but measured over 70mW so it was pushing lots of infrared.
Bottom line is you need an LPM to measure what's really going on.
I just waved my hand over it once and i can smell my skin breaking down.
Wear gloves and Goggles as well as blocking any light from a clear florescent tube. if you work with it. It's completely covered up so no light gets out unless i open it to change a sample hence my protection.
I have a small one i use to test materials exposure. It dry rots rubber bands in a day.
if you see a florescent tube that glows like one of those bug lights run or you will get arc eye if you don't have proper eye protection.
I found orange colored laser goggles to work the best since they block 190-500 some nms.