For small batches, I mix by weight. I have a cheap Harbor Freight digital scale (verified accurate to silly tolerances by me) that works very well for this. Calculate the final amount you want, divide by the ratios. Tare the container, add calculated resin amount, tare scale again , and add calculated hardener amount. Ive done less than an ounce this way, for really small home repair kinda stuff.

Dave:
Do you have epoxy and hardener in small containers that allow pouring? I did that for a while - had some 'squirt bottles' (like the mustard in a restaurant) with resin & hardener.

Now I just mix a shot at a time from the gallon cans and try to figure out how to use the whole quantity on 'something'. Once in a while,, I pay $2 or $3 for a cup of coffee - it helps to keep the 'wasted epoxy cost' in perspective. :-)