The generally ‘accepted’ dilution of standard Essential oils is 2.5% which is 15 drops of oil per 30 ml base/carrier oil. So if you are using 3 oils in a blend that would be 5 drops of each. This is perfectly safe for topical application for adults unless the essential oil carries a warning otherwise.
Some pure essential oils are very expensive, so to extend them you can create your own dilution or ‘Base Dilution’ which carries the essence of the oils in a more diluted manner. In some cases the oil itself is so strong it functions better when diluted. Oils that dilute into a BD well include Rose Otto, Sandalwood, Jasmine, Neroli, Frangipani, Tuberose and Champaca
To create a BD you should use a plain carrier oil with no fragrance itself, a good choice is Jojoba, it also lasts well. You then need to decide whether to make a 5% or 10% dilution. For 5% dilutions add 30 drops to 30 ml base oil. For 10% dilution add 60 drops to 30ml base oil.
Put your dilution into a dark bottle and store in a cool, dry place as with your other oils. Use in recipes and blends that call for the original expensive oil.