It can not only vary with the temperature and flavor, but the type of dropper you use. I find that the small glass droppers that used to come with TPA 4ml flavors would create smaller drops.
If you have Luer lock syringes, you can put a cartridge cap (if you still have any around) on the end of the syringe where the needle would screw in, and that will block the liquid from flowing out of the bottom. Drip your flavor into the syringe until you have a good measurement on how many drops per ml for that flavor and bottle/dropper. Then write it down, on the bottle or in your notebook. You can pour the flavor back into the bottle.
Like Hoosier, I have found that FA flavors come in at about 32 drops/ml. Same for the flavors from Totally Wicked in their bottles - 32. Yours may be different due to temperature, altitude, etc., but it will probably be close. I still need to measure the rate from those little plastic pipettes that TPA uses now.
For big batches I still use syringes. But if I'm making a 3ml or 5ml bottle, I find it more convenient to go with drops.