This otherwise well-written and interesting article in Slate about efforts to reform sentences for federal drug crimes begins with the following unfortunate paragraph:

In federal court, crack offenses generate sentences 100 times greater than comparable powder-cocaine crimes. In other words, while it takes 500 grams of cocaine to trigger a five-year mandatory minimum sentence, 5 grams of crack earns the same punishment.

Sentences aren't 100 times greater for crack possession; the amount necessary to trigger a given sentence is 100 times less. This ratio is seen as too high, and efforts are underway to reduce it.

A useful statistic, it seems to me, would be the amount of the drug consumed at a time. This website claims you can get one hit of crack in 1/1000 of an ounce. (It also features William F. Buckley discussing crack, which is as interesting as Alec's Buckley videos.) The ONDCP (which I do not trust) seems to suggest here that crack is sold in one tenth the amount of cocaine, roughly .1 gram to 1 gram. (These figures match up in terms of order of magnitude: .1 grams=.004 ounces.) These data suggest that a quantity ratio of 10/1 wouldn't be unreasonable for sentencing purposes. This article argues on similar grounds that 1/1 correspondence is a bad idea and would let crack dealers off too easily. The elephant in the room, of course, is that crack users are almost all minorities, leading to all the usual racial disparity problems prevalent throughout the criminal justice system. It'll be interesting to see what happens.