Every standard insulin syringe is a "U-100" syringe, meaning 1 unit = 0.01mL, so a 100-unit syringe holds exactly 1mL. Once that's fixed, the maths is three simple steps.
Step 1 — concentration: divide the peptide amount in the vial (mcg) by the volume of bacteriostatic water added (mL). A 10mg (10,000mcg) vial reconstituted with 2mL gives a concentration of 5,000mcg/mL.
Step 2 — volume needed: divide your desired dose (mcg) by that concentration. A 250mcg dose ÷ 5,000mcg/mL = 0.05mL.
Step 3 — convert to units: multiply the volume in mL by 100. 0.05mL × 100 = 5 units on the syringe.
The one counterintuitive part: adding more water doesn't change how much peptide is in the vial, only how it's spread out — more water means each unit on the syringe contains less peptide, so the same dose reads as more units. Diluting further gives finer control over small doses at the cost of using more of the syringe's scale.
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