Depends on a lot of factors...ideally, hash is stronger per gram than weed because it is made by extracting trichomes, the little THC producing glands, off the cannabis plant, (usually from the non-bud areas of the cannabis plant that would be thrown away otherwise, such as leaves and trim, ect), and compressing it in to blocks. But, depending on the extraction process, you can get different grades of hash, (best to worst:00, 0, 1, 2, 3)...the lower grades contain a lot of vegetative matter, so their potency could be considerably less than the bud produced from the plant. Also, hash is only as potent as the plant it is derrived from--a plant with mediocre potency will produce average hash at the 00 grade. A lot of street hash is SHIT because it's produced using low-grade extraction processes, (they can make more this way=more $$$).
So in conclusion, hash can be a LOT more potent than weed, but usually it isn't. *I think some people are confusing the res produced from trichome-extraction with the res produced by scrapping the shit from your pipe*
~007~