Best thing I use to measure pretty much everything is a 60 cc syringe with a blunt tip.

I have access to them because they use them for feeding tubes. But, someone told me they sell them where they sell horse stuff cuz they use it for something with horses. If not, you can get them on Amazon.

They are about a dollar each & you really only need 1. They last a very long time. You can measure even thick shampoos down to the ml.