How to read an insulin syringe
The markings are simpler than they look — once you know what U-100 actually means.
What U-100 means
U-100 is a concentration standard from insulin: 100 units per millilitre. On any U-100 syringe, the unit markings are really volume markings in disguise — 1 unit is always 0.01 mL. Draw to the 10-unit mark and you've drawn 0.10 mL of liquid, whatever that liquid is.
That's why peptide calculators output "units": it is the easiest way to name an exact position on the syringe you're holding.
The three common sizes
| Barrel size | Capacity | Typical markings |
|---|---|---|
| 0.3 mL | 30 units | every 1 unit (some every ½) |
| 0.5 mL | 50 units | every 1 unit |
| 1.0 mL | 100 units | every 2 units |
Smaller barrels spread the same units over more physical distance, so they're easier to read precisely for small draws. The scale itself never changes: 20 units is 0.2 mL on all three.
Reading a draw
Read the position of the front edge of the plunger's rubber seal — the edge closest to the needle — against the printed scale. Here is 35 units on a 100-unit syringe:
Common misreadings: judging from the seal's back edge or its middle (both overstate the draw), viewing the barrel at an angle rather than eye level, and counting tick marks without first checking what each tick represents on that particular barrel — 1 unit on some sizes, 2 on others.
Checking the number
A draw is just volume, so you can always sanity-check it: units ÷ 100 = mL. If the units you expect to draw don't match the volume your own math says a dose should be, one of the two numbers is wrong — recompute before drawing. The syringe units calculator does the conversion instantly, and the peptide calculator shows the full working from vial to units.
This guide covers reading measurements only. It is not medical advice and doesn't cover technique for administering anything.