Insulin syringes come in multiple sizes with different needle length options.
The correct size depends on your insulin dose and your comfort level with the needle size. It’s important to choose the correct size to give yourself the full dose of insulin in one shot and to avoid errors in dosing from using the wrong syringe.
You may need multiple syringes if you give different doses per day. For example, 35 units in the morning and 10 units at night means you need a 0.3-mL syringe and a 0.5-mL syringe for each dose.
Syringes also allow more flexibility if doses need to be adjusted daily based on your blood sugar levels.
If your dose is close to the maximum capacity of the syringe, you may want to go up a size to avoid problems handling the syringe.