Simple Method of Essential Oil Dilution
Always consult a certified aromatherapist or educate yourself on aromatherapy before using any essential oil. The simple safe guideline is to use 2% essential oil dilution for adults. Roughly 2% dilution is using 12 drops of essential oil to 1fl.oz. (1fl.oz. = 30 ml = approx 600 drops, 2% of 600 drops is 600 x .02 = 12 drops) of carrier oil, lotion, gel, or any moisturizer.

One drop of an essential oil could be larger or smaller depending upon the viscosity of the oil and the size of dropper or orifice reducer of the essential oil bottle.

To Determine the Number of Drops in your Blend
Total ml of carrier oil x 20 drops per ml = carrier drops
For example: 1 oz = 30 ml x 20 drops = 600 drops i.e. there are approximately 600 drops in 1oz

To Determine the Number of drops of Essential Oil
Total carrier oil drops x percent = drops of essential oil.
For example: to make a 2% solution using one ounce of carrier oil, 600 drops x .02 = 12 drops of essential oil.

Approximate Conversion Table

Dilutions are typically 2% – 10%. For adults, a 2.5% dilution is recommended and For children under 12, 1% is generally safe.

To achieve a specific dilution:

For 1 oz(30 ml, 600 drops) of Carrier Oil:
1% blend = 6 drops of essential oil per oz of carrier oil (1% of 600 drops (1 fl oz) = 6 drops)
2% blend = 12 drops of essential oil per oz of carrier oil (2% of 600 drops (1 fl oz) = 12 drops)
2.5% blend = 15 drops of essential oil per oz of carrier oil (2.5% of 600 drops (1 fl oz) = 15 drops)
3% blend = 18 drops of essential oil per oz of carrier oil (3% of 600 drops (1 fl oz) = 18 drops)
5% blend = 30 drops of essential oil per oz of carrier oil (5% of 600 drops (1 fl oz) = 30 drops)
10% blend = 60 drops of essential oil per oz of carrier oil (10% of 600 drops (1 fl oz) = 60 drops)

Measurements/conversions (by volume)
30 ml = 1 fl oz = 600 drops = 2 Tbsp
15 ml = 1/2 fl oz = 300 drops = 1 Tbsp
5 ml = 1/6 fl oz = 100 drops = 1 tsp
1 ml = 1/30 fl oz = 20 drops = 1/5 tsp

Abbreviations
ml = Milliliters, oz = Fluid Ounce, tsp = Teaspoon, tbsp = Tablespoon