Hey all,
You’d think this would be an easy question to find the answer to, but I haven’t had a lot of luck.
Here’s a 100% chocolate bar, zero added sugar,weighing 100 grams. How much caffeine does this actually have in it? It seems to be a lot easier to find out about “dark” chocolate, but I’ve seen conflicting information about this. Thanks in advance to all the smart people! 
Caffeine Informer-Hershey’s products
Google worked for me.
How Much Caffeine is in Chocolate?. Covers dark chocolate, milk chocolate, and white chocolate. It also says, properly, that different manufacturers using different recipes and differing percentages of cacao will have differing amounts so that no one answer is possible.
Don’t forget that chocolate also contains theobromine, another stimulant related to caffeine.
Cocoa powder has 12mg per tbsp(5.4g) according to google (no link; the answer in their little up top panel and mentioning multiple sources including the USDA). Since chocolate is cocoa solids (although it can be included in the form of a liquor made from the beans) fat (usually cocoa butter with no caffeine) and the sugar we’ve extracted from the equation I think that’s as close as we get unless we know how much fat we dilute the cocoa with to make “100% chocolate.”
Found it! 
I don’t know why this was so hard to find originally… the first page mentioned never came up on Google for me. Maybe the search terms were slightly different.
Anyway, it’s 198 mg. caffeine in a 100 gram bar.