Numerous conversion factors for converting one unit of matter or energy into another are available in the literature. Generally we should use these factors only when we are not able to measure the required unit ourselves, because the relation between the different units is affected by taxon, season, region and many other parameters. I.e. each species in a particular study may be unique regarding the relation between the different units, and hence using conversion factors from the literature may be introduce a bias of unknown size.
The tables below summarise some conversion factors for converting wetmass (WM) to ashfree drymass (AFDM) from different taxa and with depth gradient. The data is taken from my diploma thesis (see contact) from Kongsfjorden, Brandal (78°56'N, 11°51'E) in June-August 2003.