Converting from mg/mL to percent and back Just divide the amount in mg/mL by 10. So, if you have a 6 mg/mL e-juice, this is equal to a 0.6% e-juice. A 25 mg/mL e-juice is equal to a 2.5% e-juice. And if you had a high-strength nicotine base of 72 mg/mL, this would be 7.2% .