Interactive Tool
Reconstitution Calculator
Calculate the correct syringe units for your prescribed peptide dose after reconstitution. Enter your vial size, water volume, and desired dose to see exactly how many units to draw.
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How This Works
When you reconstitute a lyophilized (freeze-dried) peptide by adding bacteriostatic water, the peptide dissolves into solution at a specific concentration. The math to figure out how much to draw into your syringe involves two steps:
Step 1: Calculate the concentration
A U-100 insulin syringe has 100 units per 1 mL. So if you add 2 mL of water, the syringe can measure 200 total units of that solution. The concentration tells you how many micrograms of peptide are in each unit mark:
= mcg per unit
Example: 5 mg peptide + 2 mL water = 5000 mcg / 200 units = 25 mcg per unit.
Step 2: Calculate units to draw
Divide your desired dose by the concentration:
Example: 250 mcg dose / 25 mcg per unit = 10 units (0.10 mL).
Choosing your water volume
More water means a more dilute solution, which means more units per dose. This can be helpful for very small doses (easier to measure accurately on the syringe). Less water means a more concentrated solution with fewer units per dose, which is useful if you need large doses. The calculator will warn you if the calculated volume exceeds your syringe capacity or is too small to measure accurately.
Limitations
This calculator provides mathematically correct unit conversions, but real-world injection accuracy is affected by several factors:
- Needle dead space. Every needle retains a small volume of solution (typically 0.02 to 0.07 mL) in the hub after injection. For very small doses, this loss can be clinically significant. Low dead-space syringes minimize this but do not eliminate it.
- Syringe measurement precision. Standard U-100 insulin syringes have tick marks every 2 units (on 1 mL syringes) or every 1 unit (on 0.3 mL and 0.5 mL syringes). Doses that fall between tick marks require visual interpolation, which introduces measurement error of approximately 0.5 to 1 unit.
- Commercial vial overfill. Pharmaceutical manufacturers typically overfill vials by 5 to 10% to ensure the labeled amount is withdrawable. This means a "5 mg" vial may contain slightly more peptide than stated. This calculator uses the labeled amount.
- Peptide potency variation. Research-grade and compounded peptides may have purity or potency that differs from the labeled amount. Third-party certificates of analysis (COAs) can verify actual content.
- IU conversions are approximate. The relationship between international units (IU) and mass (mcg/mg) varies by peptide and assay method. The default conversion used here (3 IU per mg) is a common approximation for growth-hormone-related peptides but may not apply to your specific compound. Confirm the IU-to-mass ratio with your prescriber or pharmacist.