I use cheap plastic cups. With a little setup you only ever have to mark one cup for each size batch.

Stack a cup inside a second cup. With a measuring cup, measure two parts of water and pour into the inner cup. With the cups still stacked, use a permanent marker and mark the water level on the outside of the outer cup. Add one more part of water into the inner cup and again mark the water level on the outside cup. Now get rid of all the water. The marked cup is used only as a "gage" and epoxy is never mixed directly in it. Just drop a new cup into the "gage" cup, pour in the resin into the inner cup up to the first mark then pour in hardener up to the second mark. Lift out the inner cup mix and use. Save the "gage" cup to measure future batches. I obviously using a 2:1 mix epoxy.

Make up several different sized "gage" cups for different batch sizes. I use cocktail sized cups for wetting out and condiment sized cups for gluing.