Pen to vial calculator
A pen is a pre-filled vial with a dial on it. Enter the two numbers printed on your carton, the total milligrams and the total millilitres, and this converts a pen dose into syringe units. It also gives the water volume that makes a vial match your pen exactly, so the unit numbers you already know still apply.
Enter the figures from your own carton rather than trusting a lookup table. Device specifications differ by market and change between label revisions, and a wrong number here is worse than no number.
Mix a vial to match your pen
Reconstitute to the same concentration and every unit number you have memorised carries over unchanged, which is the safest way to switch.
| Add this much bacteriostatic water | 3.75 mL |
| Resulting concentration | 2.67 mg/mL |
| Your dose then reads | 75 units |
How this is calculated
Pen concentration is total milligrams divided by total millilitres. From there it is the same arithmetic as any reconstituted vial: volume is dose divided by concentration, and units are volume multiplied by the markings per millilitre on your syringe.
To match a vial to a pen, divide the vial's milligrams by the pen's concentration. The result is the water volume that produces an identical strength.