Measuring Small Volumes
Reconstituted peptides are measured in tiny volumes, so syringes graduated in 'units' rather than millilitres are the standard laboratory tool. Getting the unit scale right is the difference between an accurate draw and a tenfold error.
This guide explains what a unit is, how the common syringe types differ, and how to convert between millilitres and units.
What a 'unit' is
On the most common insulin syringe, U-100, the scale is defined so that 100 units = 1 mL. So 1 unit = 0.01 mL, 10 units = 0.1 mL, 50 units = 0.5 mL. The "U-100" refers to the graduation, not the syringe's volume.
The three common sizes
U-100 syringes come in three barrel volumes, and the total unit count follows directly from the volume:
- 0.3 mL = 30 units — finest resolution, best for very small draws.
- 0.5 mL = 50 units — the common middle ground.
- 1.0 mL = 100 units — for larger volumes.
Pick the smallest syringe your draw fits in: a 6-unit draw is far easier to read accurately on a 30-unit barrel than a 100-unit one.
U-100 vs U-50 vs U-40
U-50 and U-40 are different graduations: a U-40 syringe is marked so that 40 units = 1 mL, and U-50 so that 50 units = 1 mL. If you read a U-40 syringe as if it were U-100, your volume will be wrong. The safest habit is to standardise on U-100 syringes, which is what most references and our calculator assume.
Frequently asked questions
How do I convert mL to units?
On a U-100 insulin syringe, multiply millilitres by 100 — 0.1 mL is 10 units, 0.25 mL is 25 units. The calculator shows both.
Does the syringe size change the dose?
No — the amount of peptide is the same; the barrel size only changes how finely you can read the draw. Choose the smallest barrel your volume fits in.