When working with essential oils, the most common conversions you typically need are:

• 20 drops = 1 ml
• 100 drops =1 tsp = 5 ml
• 300 drops = ½ oz = 15 ml
• 600 drops = 1 oz = 30 ml

But, sometimes a little more detail is in order:

Drops	Teaspoons	Ounces	Drams	Milliliters
10 drops	1⁄10 tsp	1⁄60 oz	~1⁄8 dram	~½ ml
12 1⁄2 drops	1⁄8 tsp	1⁄48 oz	1⁄6 dram	5⁄8 ml
25 drops	¼ tsp	1⁄24 oz	1⁄3 dram	1 ¼ ml
50 drops	½ tsp	1⁄12 oz	2⁄3 dram	~2 ½ ml
100 drops	1 tsp	1⁄6 oz	1 1⁄3 dram	~5 ml
150 drops	1 ½ tsp	¼ oz	2 drams	~7 1⁄2 ml
300 drops	3 tsp	½ oz	4 drams	~15 ml
600 drops	6 tsp	1 oz	8 drams	~30 ml
24 tsp	8 tbsp	4 oz	½ cup	~120 ml
48 tsp	16 tbsp	8 oz	1 cup	½ pint
96 tsp	32 tbsp	16 oz	2 cups	1 pint

Source: Aromatherapy: A Complete Guide to the Healing Art by Kathi Keville and Mindy Green.

This chart makes the common assumption that 20 drops = 1 ml. However, always remember that drops vary in size based on liquid viscosity and the dropper or pipette you are using. If you want certainty, conduct a test with a calibrated beaker to see how many drops = 1ml.

For example, in Mandy Aftel’s book, Essence & Alchemy, she assumes that 40 drops = 1ml. Double the common assumption! I recently tested this myself using a glass eyedropper and found it to be absolutely accurate. So definitely check before moving forward with a recipe or formula.

Eden Botanicals offers a more detailed range for how many drops = 1 ml, and so far this matches my experience as well:

1 ml = 30-50 drops, depending on viscosity and size of the drop; aprox. 40-50 drops per ml for very mobile oils such as some citrus oils and fir needle oils; more viscous (thicker) oils such as Vetiver and Sandalwood will be approx. 30-40 drops per ml.

1 oz = 30 ml. Using these measurements, it can be extrapolated that there are approx. 900-1500 drops per ounce.

Notice how there are more than double the number of drops in the first estimate (600 drops = 1oz) and the Eden Botanicals estimate (900-1500 drops = 1oz)? Yikes.

This variability is why professional perfumers measure in weight with accurate lab scales. Still, if you’re just messing around at home, drops are far easier and most beginner recipes are calculated in drops. For more conversions, try this handy Volume Unit Converter site.