Published by Peptide Protocols · Reviewed September 2026 · How we make these pages · Educational & research purposes only — not medical advice.
1 mL = 100 units on a U-100 insulin syringe. Formula: mg ÷ mL = mg/mL; (mcg ÷ 1000) ÷ mg/mL = mL; mL × 100 = units.
Units to draw on a U-100 insulin syringe for the common vial sizes and water volumes. Pick the row that matches your vial and the water you added.
| Vial + water | Concentration | 250 mcg | 1 mg |
|---|---|---|---|
| 2 mg vial + 1 mL water | 2 mg/mL | 12 u | 50 u |
| 2 mg vial + 2 mL water | 1 mg/mL | 25 u | 100 u |
| 2 mg vial + 3 mL water | 0.666667 mg/mL | 38 u | 150 u |
| 3 mg vial + 1 mL water | 3 mg/mL | 8 u | 33 u |
| 3 mg vial + 2 mL water | 1.5 mg/mL | 17 u | 67 u |
| 3 mg vial + 3 mL water | 1 mg/mL | 25 u | 100 u |
| 4 mg vial + 1 mL water | 4 mg/mL | 6 u | 25 u |
| 4 mg vial + 2 mL water | 2 mg/mL | 12 u | 50 u |
| 4 mg vial + 3 mL water | 1.33333 mg/mL | 19 u | 75 u |
| 5 mg vial + 1 mL water | 5 mg/mL | 5 u | 20 u |
| 5 mg vial + 2 mL water | 2.5 mg/mL | 10 u | 40 u |
| 5 mg vial + 3 mL water | 1.66667 mg/mL | 15 u | 60 u |
| 10 mg vial + 1 mL water | 10 mg/mL | 2 u | 10 u |
| 10 mg vial + 2 mL water | 5 mg/mL | 5 u | 20 u |
| 10 mg vial + 3 mL water | 3.33333 mg/mL | 8 u | 30 u |
Worked example: a 4 mg vial with 2 mL of bacteriostatic water is 2 mg/mL. A 250 mcg draw is 0.12 mL, which is 12 units. Change the water and every number on the syringe changes — which is the single most common reconstitution mistake. The full explanation is in How to Reconstitute Peptides.
2 mL gives 2.5 mg/mL, so 0.25 mg = 0.1 mL = 10 units, 0.5 mg = 20 units, 1 mg = 40 units. 1 mL doubles the concentration and halves every unit count.
At 2.5 mg/mL it is 10 units; at 5 mg/mL it is 5 units; at 1 mg/mL it is 25 units. Always work from your own vial’s concentration — the calculator above does it instantly.
We do not recommend or partner with any peptide supplier. Use the checklist instead: third-party COAs that match your batch and lot, stated purity, clear research-use labeling, real support and proper cold-chain shipping.
The supplier checklist →Educational content only. Confirm the legal status where you live before ordering anything.
The one formula, a BAC-water chart, and the 10 most-researched beginner peptides — the math done for you. Print it for the fridge.
🎁 Send me the free cheat sheet →Every cheat sheet in the shop includes the Universal Excel Logbook — it auto-calculates reconstitution and tick marks for 38+ peptides and keeps a dated record of each vial.
Browse the cheat sheets on Etsy →