Perhaps this has come up before but I couldn't find anything about it here (not that I did a thorough search).
I read a lot of people are using pipettes and syringes for measuring the different ingredients for their liquids. Some even count droplets (which can only work if all ingredients are added from the exact same type of dropper bottle).
I find this very cumbersome and not accurate enough so I'm using a way easier method (in my opinion): a precision scale.
I keep all my ingredients (nicotine base liquid, VG, PG, distilled water, PGA and flavors) in dropper bottles.
I put my empty bottle on the precision scale (resolution of 0.01 g), zero the scale and start putting in the nicotine base liquid. I then zero the scale again (with the bottle still on it) and go to the next ingredient and so on. This is really easy and you don't waste liquid which gets left behind in your measuring tools.
To use this method you have to know the density of each of your ingredients so here's a list of them:
PGA: 0.8 - 0.9g/ml
Flavor: depends on the base of the flavor. PG based flavors are roughly the same density as PG, alcohol based flavors are roughly the same density as PGA.
Note: Some VG base liquids come pre-diluted with water (15 to 20%) to make them thinner.
If your VG base liquid is as thin as PG then it's been dilluted, resulting in a lower density.
If this is the case it's best to measure a larger amount (say 100ml) and weigh it. Divide the measured result by 100 and you know its density.
Here's an example of how a recipe translates to my method:
My VG nicotine mix has a density of 1.25g/ml so 4ml weighs 5g
VG without nicotine has a density 1.26g/ml so 4ml weighs 5.04g
Water has a density of 1g/ml so 1.5ml weighs 1.5g
My flavoring is alcohol based and has a density of around 0.9g/ml so 0.5ml weighs 0.45g
This part may seem a bit complicated to some of you but it's really easy.
I think that once you've tried this method you won't go back to using syringes and stuff.
Precision scales can be bought pretty cheap. They're not calibrated lab quality of course but they're accurate enough for this purpose. This is the one I'm using: click
I've compared it to an expensive lab model and it's pretty good!!!
Oh, and you can switch between imperial and metric system. You want to use metric (obviously).