The number of drops depends on how strong or weak your perfume is. In general, for a moderately strong aroma, we recommend adding about 10 drops of essential oil to 2 ounces of perfume base. However, this will vary according to personal preference. For example, some people prefer a lighter fragrance and in that case, you would add less than 10 drops. Others like it stronger and so they add more than 10 drops of essential oils to their perfumes.