If I have an all-grain recipe, and I want to convert it to an extract or partial-mash recipe, the easiest way is to replace the base malt with malt extract. Conversely, converting an extract recipe to all-grain involves using a base malt in place of the extract.
Is there a specific grain-to-extract ratio when doing such conversions? If it depends on the specific type of base malt, is there a table somewhere that shows the amount of potential fermentables that are available for different malts? Something that allows me to determine "X pounds of base malt == Y pounds of malt extract", and vice-versa.