What does U-100 mean on an insulin syringe?

U-100 is the syringe's scale: 100 units of its markings equal one mL. A U-40 scale fits 40 units into one mL, and a U-30 scale fits 30.

Is a syringe unit a fixed volume?

No. A unit is a fraction of a mL that depends on the scale. On a U-100 scale one unit is a hundredth of a mL; on a U-40 scale it is a fortieth of a mL.

How do I convert syringe units to mL?

Divide the units by the scale's units per mL. For example, 20 units on a U-100 scale computes to 0.2 mL.

Do syringe units say anything about the amount of substance drawn?

Not on their own. Units measure volume. Turning a volume into mg or mcg also needs the concentration in mg per mL, which the Syringe Unit Converter accepts as a separate input.

Syringe Unit Conversion: U-100, U-40 and U-30 Insulin Syringes Explained

By DoseWyz Team · 2026-10-14

The units printed on an insulin syringe are volume markings. Each scale packs a different number of units into one mL, which is what the label U-100, U-40 or U-30 states. The same reading on two different scales is two different volumes.

The Syringe Unit Converter does this conversion for any of the three scales.

The rule

Units to mL: divide the units by the scale's units per mL.
mL to units: multiply the mL by the scale's units per mL.

The scale is part of every unit figure. A unit reading without its scale does not identify a volume.

Worked example: one volume on three scales

These are illustrative round numbers, not amounts for any product.

Take a volume of 0.5 mL and express it on each scale:

U-100: 0.5 mL × 100 computes to 50 units.
U-40: 0.5 mL × 40 computes to 20 units.
U-30: 0.5 mL × 30 computes to 15 units.

One volume, three different unit readings.

Worked example: one reading on two scales

Now hold the reading fixed at 20 units and change the scale:

U-100: 20 units ÷ 100 computes to 0.2 mL.
U-40: 20 units ÷ 40 computes to 0.5 mL.

The same reading of 20 units is 0.2 mL on one scale and 0.5 mL on the other. That gap is why the converter asks for the syringe scale before it computes anything.

From units to mg and mcg

Units and mL convert with the scale alone. Getting to a mass in mg or mcg also needs the concentration of the solution. That step is covered in syringe units to mL, mg and mcg.