I don't believe there is a real "easy" way to calculate it. I think the QuickLoad software should be close but not exact. I calculate my percent fills but it is rather involved and depends on the case volume, bullet shape and seating depth, and powder density. The numbers for powder density can be found with some internet searching.
To do the calculations, you have to have a fired case with the primer still in it (or buy some sort of primer plug). The Reader's Digest version of calculating would be to weigh empty case in grams, weigh your bullet in grams, seat your bullet in the case to its normal depth and mark it with a sharpie so you can re-insert the bullet to the exact same depth later. Fill case 100% full of water and re-insert your bullet slowly to the sharpie mark forcing out water as the bullet goes down into the case. Make sure the case is dry with no water drops on the outside. Weigh the case full of water with the bullet seated to the correct depth. The calculation is: (weight of case full of water + seated bullet - weight of empty case + bullet = weight of water inside the case with a seated bullet). 1 gram water = 1 cubic centimeter of volume. Your answer is the total volume in cubic centimeters that is available for powder with that case and that bullet. Now you have to calculate what that volume is equivalent to in grains of powder.
The numbers I have seen are for VMD (Volume Measure Density which is cc/gr) and Density (gr/cc). They are inverses of each other. If you know how many grains of powder it takes to make exactly 1 cc of volume, that is Density. If you know how many cc it takes for 1 grain of powder, that is VMD. If you know one of these then you can calculate the other one. If you know density, then take 1 and divide it by the density and you get VMD. If you know VMD, then take 1 and divide it by VMD and you get density.
Here are the numbers I have for the 3 powders you mentioned:
Varget: VMD=0.0731 Density=13.680
H4350: VMD=0.0725 Density=13.791
TAC: VMD=0.0658 Density=15.198
Hope that helps.