The conversion comes down to three steps: work out the concentration of the solution, that is the amount of peptide divided by the volume of water added; convert that to micrograms per one syringe unit; then divide the number of micrograms you need by that value. This article shows the arithmetic and how the equipment works. It does not say how much peptide to take or how often, because these are substances intended for laboratory research, and decisions about any use in humans, about dose and about route belong to a doctor. The status of these preparations is set out on the legal warning page.
How do you read an insulin syringe?
An insulin syringe is graduated in units, not in millilitres. The U-100 standard, marked with an orange cap, is 100 units per millilitre, so one unit corresponds to 0.01 ml. The U-40 standard, with a red cap and used mainly in veterinary practice, is 40 units per millilitre, so one unit is 0.025 ml. The standard changes the number you read off the syringe, not the volume of liquid drawn. Mistaking a U-40 syringe for a U-100 scale gives a 2.5-fold measuring error. The rest of this article assumes the U-100 standard. Typical capacities are 0.3 ml (30 units), 0.5 ml (50 units) and 1 ml (100 units).
Step 1: work out the concentration of the solution
Concentration is the amount of peptide in the vial divided by the volume of water you added when dissolving it. For example, 5 mg of peptide and 2 ml of bacteriostatic water give 2.5 mg per millilitre, that is 2500 micrograms per millilitre. The key point is that you choose the volume of water yourself, so you set the concentration yourself. Going from 2 ml to 1 ml doubles the concentration and halves the number of units needed to measure the same amount of peptide. How to dissolve the lyophilisate is described in the article on reconstitution with bacteriostatic water.
Step 2: how many micrograms fall on one unit
On a U-100 syringe one unit is 0.01 ml, so you multiply the concentration by 0.01. At 2500 micrograms per millilitre that gives 25 micrograms per unit. The table below shows this for several combinations of peptide amount and water.
| Peptide in the vial | Water added | Concentration | Micrograms per 1 unit U-100 |
|---|---|---|---|
| 5 mg | 1 ml | 5000 mcg/ml | 50 mcg |
| 5 mg | 2 ml | 2500 mcg/ml | 25 mcg |
| 10 mg | 2 ml | 5000 mcg/ml | 50 mcg |
| 2 mg | 1 ml | 2000 mcg/ml | 20 mcg |
| 1 mg | 1 ml | 1000 mcg/ml | 10 mcg |
Step 3: convert the amount you need into units
The number of units is the amount you need in micrograms divided by the number of micrograms per unit. As a worked example with no character of a recommendation, take the figure 250 micrograms. With a solution in which one unit is 25 micrograms, 250 divided by 25 gives 10 units on the syringe. The same 250 micrograms with a solution at 50 micrograms per unit is already 5 units. Which shows that a number of units means nothing without the concentration, because it depends on how much water was added when dissolving.
The most common conversion mistakes
- Confusing millilitres with units. On a U-100 syringe, a volume of 0.5 ml is 50 units, not 0.5 units.
- Using a U-40 syringe while calculating on the U-100 scale, or the other way round. That is a 2.5-fold error in the amount measured.
- Overlooking that the volume of water used for dissolving sets everything that follows. Without a written note of “this many mg, this many ml”, no conversion is repeatable.
- Calculating on a solution past its shelf life or badly stored. Shelf life is covered in the article on storing peptides.
What this article does not do
This article does not say how much peptide to take or how often to give it. The peptides in this shop are intended for laboratory research, not for use in humans. Every decision about use, dose and route belongs to a doctor. The legal categories are discussed in the article on the legal status of peptides.
Frequently asked questions
How many units is 1 ml on an insulin syringe?
On a U-100 syringe one millilitre is 100 units, and one unit is 0.01 ml. On a U-40 syringe one millilitre is 40 units, and one unit is 0.025 ml.
How do I work out the concentration of a dissolved peptide?
Divide the amount of peptide in the vial by the volume of water added. 5 mg in 2 ml gives 2.5 mg per millilitre, that is 2500 micrograms per millilitre.
Why is the same amount of peptide a different number of units?
Because the number of units depends on the concentration, and you set the concentration yourself by the volume of water used for dissolving. Less water means a higher concentration and fewer units for the same amount of peptide.
Does this article say how much peptide to take?
No. It is purely the arithmetic of concentration and the handling of a syringe. These peptides are intended for research, and decisions about use in humans belong to a doctor.
Where this information comes from
The U-100 and U-40 standards, their cap colours, the volume corresponding to one unit and the typical syringe capacities come from insulin syringe manufacturers’ specifications. All the figures in the tables and examples are arithmetic derived from those standards, not dosing recommendations. These sources were checked on 6 September 2026.