How to Read an Insulin Syringe

Insulin syringes are marked in units, not millilitres — which trips people up when a dose is given in mcg or mL. The good news: the conversion is fixed and simple.

Units vs millilitres

A standard insulin syringe is U-100, meaning 100 units = 1 mL. That single fact covers everything:

units = mL × 100 · mL = units ÷ 100

So 1 mL is 100 units, 0.5 mL is 50 units, 0.1 mL is 10 units, and 0.01 mL is a single unit. The ratio never changes — it's built into the syringe's printed scale.

The three common sizes

U-100 syringes

0.3 mLholds 30 units

0.5 mLholds 50 units

1.0 mLholds 100 units

They all use the same 100-units-per-mL scale; the smaller barrels simply have fewer total marks, spaced further apart, which makes small volumes easier to read precisely.

Reading the barrel

Each long line is usually 10 units and each small line is 1 or 2 units depending on the syringe. You draw until the top of the plunger's rubber stopper lines up with your target mark. To turn a peptide dose into a mark, you first need the mix's concentration — then divide the dose by it and multiply by 100.

From a peptide dose to a mark

If a vial is reconstituted to 5,000 mcg/mL and you want 250 mcg, that's 0.05 mL, which is 5 units. The dosage calculator does this for any vial, water volume, and dose so you don't have to.

What a dose looks like on the syringe

Here's a 1 mL (U-100) syringe drawn to two different marks, so you can see the scale. A small peptide dose sits near the needle end; half the barrel is 50 units, or 0.5 mL.

A 250 mcg dose from a 5,000 mcg/mL mix = 0.05 mL = 5 units.

50 units is exactly 0.50 mL — half the barrel of a 1 mL syringe.

On the live calculator, this syringe fills to your calculated dose as you type, and adapts to the syringe size you pick.

Open the dosage calculator

Frequently asked questions

How many units are in 1 mL on an insulin syringe?

On a standard U-100 insulin syringe, 100 units equal 1 millilitre. So 50 units is 0.5 mL, 10 units is 0.1 mL, and 1 unit is 0.01 mL. This ratio is the same regardless of the syringe's total capacity.

What does U-100 mean?

U-100 describes the unit scale: the barrel is graduated so that 100 units fill one millilitre. A 0.3 mL syringe holds up to 30 units, a 0.5 mL holds 50, and a 1 mL holds 100 — all on the same 100-units-per-mL scale.

How do I measure 0.25 mL on an insulin syringe?

Multiply by 100: 0.25 mL is 25 units. Draw to the 25 mark. The calculator does this conversion automatically once you enter your mix and dose.

Which syringe size should I use for small draws?

Smaller-capacity syringes (0.3 mL / 30 units) have more spread-out markings, making small volumes easier to read accurately. If a dose comes out to only a unit or two, reconstituting with more water spreads it across more units.