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Pen cartridge calculator

Reusable 3 mL pens · 100 units = 1 mL · How-to guide

Your pen

Manual pen: dials up to 60 units per injection, 1 unit per click.

Dial
10 clicks
10 units on the dial = 250 mcg
Concentration
2.5 mg/mL
In the cartridge
5 mg
Doses per cartridge
19
Lasts
19 days

Load 2 mL (200 units on a syringe) from one vial. Label the cartridge with the peptide, the concentration and the date.

New to pens? Read Filling a pen cartridge and Using a pen.

Double-check every calculation before drawing a dose. This tool does arithmetic only; it is not medical advice.

How to use it

  1. Choose a mixed peptide or testosterone oil, then your pen (or the click size).
  2. Enter the vial and the water you mixed it with (or the oil’s mg/mL).
  3. Enter your dose, how much you load into the cartridge, and the priming you do.
  4. Read the clicks to dial, the dose they really give, and how long the cartridge lasts.

A worked example

A 10 mg vial mixed with 3 mL is 3.33 mg/mL. A 1 mg dose needs 30 units, so on a pen that moves 1 unit per click you dial 30 clicks, which gives 1 mg. A full 3 mL cartridge holds 10 mg; after 4 units of priming that is 9 full doses, about 9 days at one dose a day.

Doses rarely land exactly on a click. The calculator shows how far off the nearest click is and the water amount that would make your dose a whole number of clicks.

Before you fill a cartridge

A filled cartridge of mixed peptide is a mixed vial with a needle-pierced stopper, so it follows the same limit: the label’s where there is one, otherwise the common practice of 28 days in the fridge. Testosterone oil isn’t mixed, and oil should never go in an auto-injecting pen (it pushes too fast for thick oil).

Step by step: filling a 3 mL cartridge and using a reusable pen.

Questions

How many units is one click?
Most reusable insulin-style pens (V-pens, Gansulin) deliver 1 unit per click, where 100 units = 1 mL. Some pens move 2 units per click; pick yours in the calculator.
Why does my dose land between clicks?
Clicks are whole steps, so a dose of 7.5 units can’t be dialed exactly on a 1-unit pen. The calculator shows the nearest click and the dose it really gives, and the water amount that would put your dose exactly on a click.
What is priming and how much does it waste?
Priming pushes air out of a new needle and cartridge before the first dose; some people also do a small safety shot before each dose. Both use liquid, so the calculator takes them out of the doses per cartridge.
How long can a filled cartridge be used?
A cartridge of mixed peptide is a mixed vial: follow the label where there is one, otherwise the common practice of 28 days in the fridge. The calculator warns when a cartridge would last longer than that. Testosterone oil isn’t mixed, so the limit doesn’t apply.

Example numbers show how the math works; they are not dose recommendations. Check every draw against your own vial and your prescriber’s instructions.