Peptide Science
Peptide Science
Reference

Syringe Unit Conversions

May 02, 2026
conversioniumcgmginsulin-syringereference

Mass-and-volume conversions that come up at the bench. For why the math works, see Syringe, Draw and Dosage Math. For per-vial reconstitution math, see Reconstitution Cheat Sheet. For an interactive version, the peptide calculator handles arbitrary vial / volume / dose combinations.

Mass: mcg, mg, IU

UnitEquivalentWhere it shows up
1 mg 1000 mcg Vial labels (e.g., "5 mg vial"); peptide reference doses.
1 mcg 0.001 mg Per-dose ranges for most peptides (Ipamorelin 100 mcg, BPC-157 250 mcg).
1 g 1000 mg = 1,000,000 mcg Bulk reagent quantities; not used for individual peptide dosing.

Volume: mL, units (U), drops

UnitEquivalentWhere it shows up
1 mL 100 U on a U-100 insulin syringe Standard insulin-syringe convention; 1 mL of solution = 100 unit marks.
1 U 0.01 mL The smallest reliable mark on a U-100 insulin syringe.
1 mL ~20 drops (standard dropper) Intranasal sprays - manufacturer-specific; check the label.

Reading insulin-syringe units: each numbered mark is 5 U on most U-100 syringes; each minor tick is 1 U. The plunger's leading edge against the mark is what counts, not the trailing edge of the rubber stopper. Eye level on a flat surface, not at an angle.

The HGH IU-vs-mg gotcha

IU (International Units) is a potency measure, not a mass measure. For most peptides this distinction is irrelevant - they're labelled in mcg or mg. For somatropin (recombinant human GH), the convention is mixed and the conversion matters:

SomatropinEquivalentNote
1 IU ~0.33 mg (333 mcg) The WHO-defined ratio for rhGH (3 IU = 1 mg).
3 IU 1 mg Common bodybuilding dose unit - 2–3 IU/day = 0.67–1 mg/day.
5 IU ~1.67 mg Higher-end recreational dosing.
10 IU ~3.33 mg Per-vial common pack size (10 IU = ~3.33 mg per vial).

Why this matters: a "10 IU vial" of HGH is a 3.33 mg vial. Reconstitute with 1 mL BAC water and you get 10 IU per mL = 0.1 IU per insulin-syringe unit. A 2 IU dose is 20 units on the syringe.

Common per-dose conversions (worked examples)

DoseVial / reconUnit marks
100 mcg Ipamorelin 2 mg vial in 2 mL β†’ 10 mcg/U 10 U
250 mcg BPC-157 5 mg vial in 2 mL β†’ 25 mcg/U 10 U
500 mcg TB-500 5 mg vial in 5 mL β†’ 10 mcg/U 50 U
1.75 mg PT-141 10 mg vial in 2 mL β†’ 50 mcg/U 35 U
2 IU somatropin 10 IU vial in 1 mL β†’ 0.1 IU/U 20 U

Common mistakes

  • Reading mL when the syringe is in U. A "1 mL" insulin syringe is graduated to 100 U, not 100 mL. The numbered marks are units. Read what's printed.
  • Confusing IU with mcg for non-HGH peptides. Outside of HGH and a couple of approved drugs (insulin), peptides are dosed in mcg or mg. "100 IU of BPC-157" is a category error - there's no IU definition for it.
  • Using HGH's 3:1 IU-mg ratio for other peptides. The ratio is specific to rhGH. Other peptides where IU sometimes appears on labels (insulin, oxytocin) have different ratios. When in doubt, use the mcg / mg labelling on the vial.
  • Counting from the wrong end of the plunger. Leading edge against the unit mark, not trailing edge. The black rubber stopper has a small bevel; the leading edge is the flat side closest to the needle.

Cross-references

Syringe Unit Conversions