An insulin syringe is marked in units, not millilitres — and a "unit" is a slice of volume, not an amount of drug.
U-100 means 100 units per millilitre: 1 mL = 100 units, 0.1 mL = 10 units, 0.01 mL = 1 unit.
U-50 and U-30 syringes hold 50 and 30 units per mL — smaller barrels with finer marks for tiny draws.
How much compound sits in one unit depends entirely on your concentration.
To convert a dose: draw volume = dose ÷ concentration, then units = draw volume × 100.
An insulin syringe is marked in units, not millilitres — and a "unit" is a measure of volume, not of drug. In plain terms: the number you draw to is a slice of liquid, and how much compound is in that slice depends on how you mixed the vial. Understanding the mapping between units and millilitres is the key to translating a dose into the mark you draw to.
What U-100 means
The "U-100" designation is a standard: 100 units per millilitre1. So:
1 mL = 100 units
0.5 mL = 50 units
0.1 mL = 10 units
0.01 mL = 1 unit
U-50 and U-30 syringes hold 50 and 30 units per millilitre respectively; they're just smaller barrels with finer graduations, useful for very small draws.
Units are about volume, not dose
Because a unit is a fixed slice of volume, the *amount of compound* in one unit depends on your concentration:
`` compound per unit = concentration (mg/mL) ÷ 100 ``
At 2.5 mg/mL, one unit contains 0.025 mg = 25 mcg. So a 250 mcg dose is 10 units. Change the concentration and the same 10 units delivers a different amount. In plain terms: the syringe measures volume; the concentration decides what that volume is worth.
Count the major graduations (often every 10 units) and the minor ticks between them. Draw slowly and read at eye level with the plunger tip. If your dose lands between ticks routinely, that's a sign to reconstitute at a lower concentration so draws fall on cleaner marks — see how to reconstitute a peptide.
Frequently asked
How many units are in 1 mL?
On a U-100 syringe, 1 mL = 100 units, so 0.1 mL = 10 units and 0.5 mL = 50 units. On a U-50 syringe 1 mL = 50 units; on a U-30, 1 mL = 30 units.
Is a "unit" a dose?
No. A unit is a volume mark on the syringe, not an amount of compound. How much compound a unit contains depends entirely on your concentration.
Which syringe size is best for tiny draws?
A U-50 or U-30 syringe has the same 0.01 mL-per-unit scaling on a smaller barrel, so the graduations are physically further apart and easier to read for very small volumes. The number of units for a given dose does not change — only how spread out the marks are.
References
International Organization for Standardization ISO 8537: Sterile single-use syringes, with or without needle, for insulin — defines the U-100 graduation standard of 100 units per millilitre.ISO. 2016. ISO 8537:2016
Zyra Labs is a research and educational utility. Nothing on this page is medical advice, a dosing recommendation, or an endorsement of any compound. We never sell or source compounds and refuse sourcing questions. Consult a qualified clinician for decisions about your health.