Pen click calculator
For reusable cartridge pens that dispense a fixed volume per dial step. Enter the cartridge's mass and volume and the step volume from the pen's manual.
Each click holds
33.3 mcg
3.333 mg/mL · 300 clicks per cartridge
The arithmetic
- 1. 10 mg ÷ 3 mL = 3.333 mg/mL
- 2. 3,333.3 mcg/mL × 0.01 mL = 33.3 mcg per click
- 3. 3 mL ÷ 0.01 mL = 300 clicks
Math only. Priming shots and the volume left in the cartridge are not counted, so real counts are lower.
By [Author name]. Licensed pharmacist review: pending. Last updated .
How pen math differs from syringe math
A syringe measures any volume along its scale. A pen only moves in fixed steps, so every result has to be a whole number of clicks. The calculator shows the exact click count and, when it is fractional, the mass the nearest whole click count actually holds.
Many reusable pens dial in U-100 units, where one click is 0.01 mL, the same as one unit on a U-100 syringe. Others dial in different steps. The step volume is a property of the pen, which is why this calculator never assumes it from a brand name.
For syringes, use the main calculator. For multi-peptide vials, use the blend calculator.
Pen calculator questions
How do you work out what one pen click holds?
Concentration (cartridge mg ÷ cartridge mL) × volume per click. A 3 mL cartridge holding 15 mg is 5 mg/mL; at 0.01 mL per click, one click holds 50 mcg.
How many clicks are in a cartridge?
Cartridge mL ÷ mL per click. A 3 mL cartridge at 0.01 mL per click is 300 clicks, before priming and the volume that stays in the cartridge.
Can I count clicks on a prefilled prescription pen?
Prefilled prescription pens are designed and labeled to deliver specific doses, not click-counted fractions, and their click volumes are not published as a dosing scale. This site does not convert brand pens. For questions about a prescribed pen, ask the prescriber or pharmacist.