Shortfill Vape Juice UK: How Does the Mixing Sum Work? A shortfill is nicotine-free e-liquid in a bottle bigger than 10ml, with room left so you can add nicotine shots if you want to. The mixing sum is simple: total milligrams of nicotine divided by total millilitres gives the final strength in mg/ml. Check your kit's manual first, because not every device suits shortfills, and remember the 20mg/ml limit. Single-use vapes have been banned since 1...