U-100, U-50, U-30 units: reading your insulin syringe

On an insulin syringe, the graduations are not in millilitres but in units (IU). This is a classic source of confusion. Understanding the U-100 / U-50 / U-30 system lets you draw a precise volume without a calculation error.

What does "U-100" mean?

"U-100" means 100 units per millilitre. The correspondence is therefore fixed:

1 IU = 0.01 ml (and 100 IU = 1 ml).

A 1 ml U-100 syringe is graduated from 0 to 100 IU. Drawing "20 IU" means drawing 0.20 ml.

U-100, U-50, U-30: what's the difference?

All three use the same system (100 IU/ml), but different capacities:

• U-100 (1 ml): up to 100 IU. Versatile.
• U-50 (0.5 ml): up to 50 IU. Graduations more spread out.
• U-30 (0.3 ml): up to 30 IU. The finest reading.

The smaller the syringe, the more spread out the graduations for a given volume — so the more precise the reading of a small volume. To draw 8 IU, a U-30 will read more clearly than a U-100.

Converting a volume into units

The volume to draw depends on the concentration of your reconstituted solution. The approach:

1. Calculate the concentration (see the guide How to reconstitute a peptide).
2. Work out the volume needed for the amount you want.
3. Convert that volume into units: IU = volume in ml × 100.

Example: at 5 mg/ml, drawing 250 mcg (0.25 mg) requires 0.05 ml, i.e. 5 IU.

To avoid manual math, the reconstitution calculator shows the volume and the units on the chosen syringe directly.

Choosing the right syringe

• Small, regular volumes → prefer a U-30 or U-50 for precision.
• Needles: protocols commonly describe 29G to 31G, short (4 to 8 mm) for the subcutaneous route.
• A new, sterile syringe for each handling.

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Above all, remember the constant 1 IU = 0.01 ml. From there, every reading becomes a simple conversion. The glossary details the other terms (concentration, mcg, half-life).