How to Read an Insulin Syringe: 0.3 ml, 0.5 ml & 1 ml Markings Explained

The one rule: 100 units = 1 ml

Every U-100 insulin syringe uses the same scale regardless of size: 100 units per milliliter. A smaller syringe does not use smaller units — it just has a shorter barrel with finer, more readable lines. 10 units is 0.1 ml on all of them.

Reading each size

1 ml syringe (100 units): lines every 2 units, numbers every 10. The barrel is long and the lines are close together, so small doses (under 10 units) are hard to read precisely.

0.5 ml syringe (50 units): lines every 1 unit, numbers every 5. The best general-purpose size for peptide doses between 10 and 50 units.

0.3 ml syringe (30 units): lines every 1 unit, and 'demi' versions mark every half unit. The choice for small doses — 250 mcg BPC-157 at 10 units, 100 mcg CJC-1295 at 5 units — where a single line is a meaningful fraction of the dose.

Where to read the plunger

Read the dose at the edge of the black rubber stopper closest to the needle — the flat face, not the rounded tip or the far end of the stopper. Hold the syringe at eye level; reading from above or below shifts the apparent line by a unit or more on a 1 ml barrel.

Drawing an exact dose

Draw air equal to the dose, inject it into the vial (this keeps pressure neutral), invert the vial, and pull the plunger slightly past the target. Tap the barrel so bubbles rise to the needle, then push the plunger up to the exact line — expelling the air and excess liquid back into the vial. A bubble the size of a unit is a unit of missing dose.

From units back to your dose

Units measure volume, so the peptide amount in each unit depends on how the vial was mixed: mcg per unit = vial mcg ÷ (water ml × 100). A 5 mg vial in 2 ml water gives 25 mcg per unit; the same vial in 1 ml gives 50 mcg per unit. If a protocol says 'take 10 units', it only means something for the concentration it was written for.