Nah man, just looking at the pads of bristol I've got sitting around:
>canson 100lb, 225gsm
>canson xl, 96lb, 260gsm
>bienfang 146lb, 238gsm
Basis weight isn't based on the final sheets you get, it's based on the uncut stock, so unless you know how big those sheets were, it's useless. Office paper this isn't a problem, it's all normalized to a few sizes and well labeled.
With art paper it's a complete crapshoot.