How much water should I add?
Add enough water that your usual dose lands between 10 and 40 units on the dial, and on a whole click. For a 10mg vial and a 250mcg dose, 2ml gives you exactly 5 clicks. Choose the water volume before you mix, because afterwards you are stuck with it.
Why the water volume is the only real decision
Reconstituting is just adding water to a powder. The only choice you make is how much, and that choice sets everything else: how many clicks a dose takes, how precisely you can hit it, and how much you waste if you get it wrong. Nothing you do afterwards can change it without starting again.
More water means a bigger number on the dial. A bigger number is more forgiving, because being one click out matters less when the dose is 30 clicks than when it is 3. Less water means fewer clicks and a more concentrated liquid, which suits a small cartridge but leaves no margin.
The arithmetic, once
Divide the vial in milligrams by the water in millilitres to get the concentration. Multiply by 1,000 to get micrograms per millilitre. One click is 0.01ml, so divide by 100 to get micrograms per click. Then divide your dose by that.
| Vial | Water | Per click | 250mcg dose | 500mcg dose |
|---|---|---|---|---|
| 5mg | 1ml | 50mcg | 5 clicks | 10 clicks |
| 5mg | 2ml | 25mcg | 10 clicks | 20 clicks |
| 10mg | 1ml | 100mcg | 2.5 clicks | 5 clicks |
| 10mg | 2ml | 50mcg | 5 clicks | 10 clicks |
| 10mg | 3ml | 33.3mcg | 7.5 clicks | 15 clicks |
| 15mg | 3ml | 50mcg | 5 clicks | 10 clicks |
Look at the 10mg with 1ml row. A 250mcg dose comes to 2.5 clicks, and a pen cannot do half a click. That single row is the mistake most people make, and it is only visible before you mix.
Picking a number in practice
Start with your dose
Work in micrograms. Whatever you plan to take per injection is the number everything is built around.
Aim for 10 to 40 clicks
That band is the sweet spot. Comfortably readable on the dial, well inside the pen's 60-unit limit, and forgiving if you are a click out.
Check it lands whole
Run the number. If it comes out at 7.5 clicks, nudge the water up or down until it is a whole number. The calculator does this and tells you the exact water volume that fixes it.
Check it fits the cartridge
A 3ml cartridge is the hard ceiling. If your water volume exceeds 3ml you will need two cartridges from one vial, which is fine, just plan for it.
Adding the water without ruining it
Run the water slowly down the inside wall of the glass so it pools underneath the powder rather than hitting it directly. Firing a jet straight into the powder is the most common way to damage a batch. Then leave it alone for a few minutes and let it dissolve on its own.
Never shake it. If anything is still sitting there after a few minutes, roll the vial gently between your palms. Cloudiness, stringiness or anything that will not dissolve means something has gone wrong, and no amount of agitation fixes that.
Questions
- Can I add more water later?
- You can physically, but you should not. You would be adding water to an already reconstituted liquid, which means recalculating everything and introducing another opportunity for contamination. Work out the volume first.
- What if I used the wrong amount of water?
- Nothing is ruined. Recalculate at the concentration you actually have, and use whatever the dial says now. The only real problem is if the new number is a fraction of a click or over the pen's 60-unit limit.
- Does more water make it weaker?
- It makes the liquid more dilute, so a given dose takes more clicks. The amount delivered per dose is identical if you dial correctly. Dilution changes the arithmetic, not the quantity.
3ml Glass Cartridge
One 3ml refill cartridge.