Only a hobby cue maker, but i've been using about 5 gals of WEST a year for the past 30 years for other millwork. IOW, I buy it in C units.
You have not actually stated what your problem is?
The best way is as Joey describes. Actual weight.
If you use the pumps, be careful of 3 things. 1.) the pumps are all the same units 2.) The pumps are always put in the correct container, resin in resin, hardener pump in one of the hardeners. The pumps are different size between resin and hardener. Don't mix them up. 3.) the pumps are always primed and yielding a full dose. No more, no less.
The pump packs sometimes include a 3:1 pump for the new laminating resin. Throw it out. Or at least don't get it mixed up with the 105/205/206 family, which is 5 resin to 1 hardener.
This can make pumps a problem for people using small quantities. The pump loses prime, you start guessing how to make it up, it all goes wrong. If you use pumps & use them after lapses, get used to squirting a shot in a clean empty cup to be sure the prime is good, before shooting into your mixing container. I just throw the primer shots out, but they can be returned to the can.
WEST sells pumps separately. I keep a few packs on hand for when one goes bad and won't hold a prime. Again, just make sure the pumps are all the same unit. You can still use them in any size can; so long as the resin pump goes in the resin, and the hardener pump in one of the hardeners.
You can mix 205 with 206, say by alternating shots.
I pump one shot resin, one shot hardener, in that order, all the time. Then i don't lose count, even if going to 15 or 20 shot of each mix. But within that, you can choose to go 1 shot resin, one shot 205, 1 shot resin, 1 shot 206, or any sequence desired. In the summer you probably only want the slow stuff. In winter maybe only the fast stuff depending on shop heat. Sometimes a mix makes sense on a large glue-up.
Per WEST advice, i always use some cotton flocking in the mix. Does not have to be a lot; but especially on dense cue woods it can help prevent starved joints. Always thoroughly mix the epoxy, before adding any fillers.
Even if using pumps to dispense, for small quantities i'd stick to Joey's method of keeping track of weight on a scale. Tare out the scale with the empty mixing container so it is not a factor in the weight calc.
You probably already know this, but just in case: People who come from mixing fiberglass resins might not take the mix ratio seriously for epoxy. For vinyl or polyester resin for fiberglass, if you want it to set slow, you use less hardener. Fast, you add a little more.
This flat does not work for any epoxy type. The ratio is critical. WEST says a little under for the hardener won't hurt. A little too much, and you have an uncured oxidizer eating away in the mix of whatever is being built; plus the bond will be weaker.
Good luck!
smt