Units, millilitres and micrograms
A unit is 0.01ml. One click on the pen is one unit. Units are a measure of volume, micrograms are a measure of quantity, and the concentration of your mix is what converts between the two. Mixing those last two up is where most dosing errors start.
The three measurements
Millilitres measure how much liquid there is. Micrograms measure how much substance is in that liquid. Units are just a convenient name for one hundredth of a millilitre, borrowed from insulin syringes, because 0.05ml is harder to say than 5 units.
| Measurement | What it measures | Fixed? |
|---|---|---|
| Millilitre (ml) | Volume of liquid | Yes, always the same |
| Unit | Volume: 0.01ml | Yes, always the same |
| Click | One unit on the dial | Yes, on every pen we sell |
| Microgram (mcg) | Quantity of substance | No, depends on your mix |
| Milligram (mg) | 1,000 micrograms | No, depends on your mix |
The right-hand column is the whole lesson. Units are a fixed measure of volume. Micrograms are not fixed to units by anything except the concentration you chose when you added the water.
Why 'how many units is 250mcg' has no single answer
It is like asking how many spoonfuls make a cup of coffee without saying how strong the coffee is. If a millilitre holds 5,000mcg, then 250mcg is 5 units. If it holds 10,000mcg, the same 250mcg is 2.5 units. Same dose, different volume, because the liquid is a different strength.
Whenever someone quotes a number of units without also saying their vial size and water volume, that number is meaningless to anyone else. So never copy somebody else's click count.
Converting, in both directions
- Micrograms per millilitre = vial in mg ÷ water in ml × 1,000
- Micrograms per click = micrograms per millilitre ÷ 100
- Clicks for your dose = dose in mcg ÷ micrograms per click
- Millilitres per dose = clicks × 0.01
Worked through: a 10mg vial in 2ml is 5,000mcg per ml, so 50mcg per click. A 250mcg dose is 250 ÷ 50, which is 5 clicks, which is 0.05ml. Every calculation in this hobby is that one, repeated.
1mg is 1,000mcg
Vials are labelled in milligrams and doses are usually discussed in micrograms, so you will be converting constantly. Move the decimal point three places. 0.25mg is 250mcg. 2.5mg is 2,500mcg. Getting this wrong by a factor of a thousand is the worst error available, and it happens.
Questions
- Is a unit the same on every pen?
- On every pen we sell, yes: one unit is one click is 0.01ml. It is the same scale as a U-100 insulin syringe. Always check any other pen, because a different increment would change every number.
- Why do people say clicks instead of units?
- Because you can count clicks without looking at the dial, which matters when the pen is against your skin. They are the same thing.
- How many units in 1ml?
- One hundred. So a full 3ml cartridge holds 300 units.
Duihao V3 Reusable Pen
Reusable metal pen with a closed cap and pocket clip.