How do I convert mcg to units on an insulin syringe?

Units are a volume, not a mass. A U-100 insulin syringe is marked so that 100 units is one millilitre, so a unit is one hundredth of a millilitre regardless of what is dissolved in it. Micrograms are a mass of peptide. Converting between them needs the concentration, which is the vial size divided by the bacteriostatic water added, and that is why the calculator asks for both.

Does the amount of bacteriostatic water change the dose?

Nothing about the dose changes, only the volume it arrives in. Reconstituting a 5mg vial with 2ml gives 2.5mg/ml, so a 250mcg dose is 10 units. The same vial with 4ml gives 1.25mg/ml, and the same 250mcg dose becomes 20 units. Both deliver 250mcg. More water makes a dose easier to measure accurately and makes the vial run out in fewer doses.

What does it mean if my dose lands between syringe marks?

It means the dose falls between the marks printed on the syringe, so drawing it accurately depends on judging a gap by eye. Whole units are easy to hit, halves are workable, and anything else is guesswork. It is not dangerous by itself, but it is avoidable: choosing a different water volume when the vial is mixed will usually move the same dose onto a readable mark.

Does this recommend a dose?

No. This page converts numbers you enter into a volume on a syringe. It does not suggest a dose, a compound or a schedule, and no part of it returns a dose. What dose is appropriate is a question for a clinician.

Peptide dose calculator

Your vial is already mixed. This turns the dose into units on the syringe.

Vial sizemgmg in the vialBacteriostatic watermlwhat you already addedYour dosemcgthe dose you are taking

Draw

10 units

5mg in 2ml is 2.5mg/ml, so 250mcg is 0.1ml, which is 10 units on a U-100 syringe.

Concentration: 2.5 mg/ml
Volume: 0.1 ml
Syringe mark: whole unit

Have not added the water yet? The reconstitution calculator picks a water volume for you, so the dose lands on a mark you can read and the vial does not expire with doses left in it.

Why a unit is not a milligram

A U-100 insulin syringe is marked in units of volume, where 100 units is one millilitre. A unit is therefore one hundredth of a millilitre no matter what is dissolved in it. The number printed on a peptide vial is a mass in milligrams, and mass and volume are only related once the peptide is dissolved in a known amount of liquid. That relationship is the concentration, and it is why no calculator can convert a dose to units without being told how much bacteriostatic water went in.

The same dose can be two different numbers of units

A 5mg vial reconstituted with 2ml holds 2.5mg per millilitre, so a 250mcg dose is 0.1ml, which is 10 units. The identical vial reconstituted with 4ml holds 1.25mg per millilitre, and the identical 250mcg dose becomes 0.2ml, or 20 units. Both draws deliver exactly 250mcg of peptide. This is the single most common source of confusion when someone compares their syringe to another person's, and neither of them is wrong: they diluted differently.

Questions

How do I convert mcg to units on an insulin syringe?: Units are a volume, not a mass. A U-100 insulin syringe is marked so that 100 units is one millilitre, so a unit is one hundredth of a millilitre regardless of what is dissolved in it. Micrograms are a mass of peptide. Converting between them needs the concentration, which is the vial size divided by the bacteriostatic water added, and that is why the calculator asks for both.
Does the amount of bacteriostatic water change the dose?: Nothing about the dose changes, only the volume it arrives in. Reconstituting a 5mg vial with 2ml gives 2.5mg/ml, so a 250mcg dose is 10 units. The same vial with 4ml gives 1.25mg/ml, and the same 250mcg dose becomes 20 units. Both deliver 250mcg. More water makes a dose easier to measure accurately and makes the vial run out in fewer doses.
What does it mean if my dose lands between syringe marks?: It means the dose falls between the marks printed on the syringe, so drawing it accurately depends on judging a gap by eye. Whole units are easy to hit, halves are workable, and anything else is guesswork. It is not dangerous by itself, but it is avoidable: choosing a different water volume when the vial is mixed will usually move the same dose onto a readable mark.
Does this recommend a dose?: No. This page converts numbers you enter into a volume on a syringe. It does not suggest a dose, a compound or a schedule, and no part of it returns a dose. What dose is appropriate is a question for a clinician.

This page calculates. It does not prescribe, and nothing here is a recommendation to take anything.