In this article
Cartridge pens and insulin syringes are marked in units on a U-100 scale. Knowing what a unit means makes the mg and ml math easy to follow.
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What a unit is
Units-to-millilitres conversion (U-100 scale)
On a U-100 syringe the unit scale and the millilitre scale are the same line: 100 units fill exactly 1 mL, so every unit is 0.01 mL. Use this chart to convert in either direction.
| Volume | Units (U-100) |
|---|---|
| 0.01 mL | 1 unit |
| 0.05 mL | 5 units |
| 0.10 mL | 10 units |
| 0.25 mL | 25 units |
| 0.50 mL | 50 units |
| 1.00 mL | 100 units |
- How many units is 1 mL? On a U-100 syringe, 1 mL is 100 units.
- How many units is 0.1 mL? 0.1 mL is 10 units.
- How many mL is 1 unit? 1 unit is 0.01 mL.
- How many units is 0.5 mL? 0.5 mL is 50 units.
These conversions only hold on a U-100 syringe (100 units per mL). A U-40 syringe uses a different scale, so confirm the barrel before relying on the numbers.
Understanding the U-100 Scale
The U-100 scale is a standard way of marking tiny liquid amounts on a syringe or pen. On this scale, 1 unit = 0.01 ml. So 10 units is 0.10 ml, 50 units is 0.50 ml, and 100 units is 1.00 ml.
A standard 3 ml cartridge holds 300 units of liquid. The Gansulin pen dials from 1 to 60 units, one click at a time.
Units measure volume, not strength
A unit tells you how much liquid you have. It does not tell you how much compound is in that liquid. How much compound is in a given volume depends on the concentration (the strength of the mixture) you prepared in the lab.
Think of it like making a drink from powder. The cup size tells you how much liquid you have. Whether the drink is strong or weak depends on how much powder you stirred in. Units work the same way.
Concentration is just the milligrams of powder divided by the milliliters of liquid you added.
Key point: A unit is a measure of liquid volume, not the strength of the compound itself.
From units to milligrams
Reconstitution Example
Here is a worked example. Say you reconstitute (dissolve the powder in liquid) a 10 mg vial with 1 ml of bacteriostatic water (a sterile water used in lab work to dissolve powders safely):
- Concentration = 10 mg ÷ 1 ml = 10 mg/ml.
- Draw 10 units = 0.10 ml = 0.10 × 10 = 1 mg.
- Draw 5 units = 0.05 ml = 0.5 mg.
Change how much water you add, and the concentration changes too. Add 2 ml instead of 1 ml, and the same vial becomes 5 mg/ml. Now 10 units equals only 0.5 mg.
Let the calculator do it
Our free peptide calculator converts between mg, ml, and units in seconds. The protocol planner also estimates how many vials a given schedule will need.
Pair it with the right bacteriostatic water and cartridges.
Preppin Peppers sells laboratory hardware and consumables for research, educational, and demonstration use only. This article is general educational information about equipment and does not describe, recommend, or instruct the use of any peptide or other substance in humans or animals. Nothing here is medical advice.
Reminder: research and educational reference only. Preppin Peppers sells hardware and materials, not peptides. Not medical, dosing, or health advice, not evaluated by the FDA, and not intended for human or animal use.
Frequently asked questions
How many ml is 1 unit on a U-100 syringe?
On a U-100 scale, 1 unit = 0.01 ml. So 10 units = 0.10 ml, 50 units = 0.50 ml, and 100 units = 1.00 ml. A standard 3 ml cartridge holds 300 units total.
How do I convert units to milligrams for a reconstituted vial?
Divide the vial's total mg by the ml of solvent added to get mg/ml concentration, then multiply by the drawn volume in ml (units × 0.01). Example: 10 mg/ml × 0.10 ml = 1 mg.
Does a unit on a syringe tell me how much compound I have?
No. A unit measures liquid volume only. The milligrams present depend on concentration, the mg of powder divided by the ml of solvent used during reconstitution. Change the solvent volume and concentration changes too.
What the research community gets wrong about reading units, milliliters, and milligrams on a U-100 scale
The U-100 scale is simple math, but a few mix-ups show up again and again at the bench. Here are the ones worth clearing up.
- Treating a unit as an amount of compound. A unit on a U-100 barrel is a mark for liquid volume (1 unit = 0.01 ml), not a measure of how many milligrams of powder are in the draw. The milligrams depend entirely on the concentration you prepared.
- Assuming "10 units" is the same across every vial. Two vials reconstituted at different concentrations give very different milligrams for the same 10-unit mark. The number on the barrel never changes, but the mg it represents does.
- Reading "U-100" as the compound's strength. U-100 just means the scale is calibrated so 100 units equals 1 ml of liquid, whatever is dissolved in it. It says nothing about your peptide. The FDA-labeled insulin standard is where the 100 units/ml calibration comes from, and the scale carries that same geometry regardless of contents.
- Forgetting to redo the math when solvent volume changes. Add 2 ml of bacteriostatic water instead of 1 ml and the concentration halves, so the same unit mark now represents half the milligrams. Any change in how much water you add means recalculating before you read the scale.
- Confusing the volume mark with a biological "unit." The insulin unit is a measure of biological activity, but on a research bench the U-100 tick is only a volume reference. For a reconstituted powder, the mark means 0.01 ml per unit and nothing more.
From our bench: Next time you reconstitute a vial, note the concentration you prepared (mg of powder divided by ml of water added), then dial or draw a specific unit mark and record the milligrams that mark works out to on your U-100 scale. If you have a fine analytical balance, weigh the drawn volume and compare it to the 0.01 ml per unit the scale predicts. Send us your concentration, your unit count, and the calculated mg (real numbers only, no estimates) and we will add measured examples to this guide.
Sources
- Bacteriostatic Water for Injection, USP , FDA/DailyMed label (0.9% benzyl alcohol)
- Duerkop et al., Biotechnol J 2018 , Impact of Cavitation, High Shear Stress and Air/Liquid Interfaces on Protein Aggregation
- Sigma-Aldrich (Merck) , Handling and Storage Guidelines for Peptides and Proteins
- DailyMed (FDA) , Humulin R (insulin human) U-100 label, 100 units/mL
- NIST Office of Weights and Measures , SI Units: Volume (milliliter as the cubic centimeter)
✔ Reviewed by Bryan Le, PharmD, RPh
Bryan is a licensed pharmacist (Doctor of Pharmacy, Registered Pharmacist). Reconstituting lyophilized preparations is core pharmacy practice, so he reviews The Lab’s content for technical accuracy and to keep it within a research-and-education scope, with no medical or dosing advice. View profile on LinkedIn.
