The Darlkroom cookbook, 2. ed. has tables on this from page 265 onwards, just punch the numbers into any 4-banger calculator.....

More importantly it has a very important table at page 275 : Teaspoon conversions, solving the riddle a certain blogger has been struggling with......
Anyone familiar with homeloading ammo will know that volumetric measures, like teaspoons and such is more than accurate enough to measure out very small amounts of powder.