This peptide calculator handles both steps of preparing a lyophilized (freeze-dried) peptide: reconstitution — how concentrated your solution becomes after adding bacteriostatic water — and dosing — how many units to draw on a standard U-100 insulin syringe. Enter the milligrams of peptide in the vial, the volume of BAC water you add, and your target dose, and it returns the syringe units, injection volume, concentration, and how many doses the vial holds.
Getting the mixing math right matters because peptides are dosed in micrograms while syringes are marked in units, so a small arithmetic slip changes the dose several-fold. This tool is provided for educational purposes only and does not replace guidance from a licensed pharmacist or healthcare provider.
How Peptide Reconstitution Works
Reconstitution means dissolving a dry peptide with bacteriostatic water to make an injectable liquid. Two simple relationships drive the whole peptide reconstitution calculation:
- Concentration (mg/mL) = peptide in vial (mg) ÷ BAC water added (mL)
- Dose volume (mL) = desired dose (mg) ÷ concentration (mg/mL)
Because a U-100 insulin syringe holds 100 units per milliliter, units to draw = dose volume (mL) × 100. Adding more water does not change how much peptide you inject — it only spreads the same peptide across a larger volume, making each unit easier to measure precisely. A lower concentration (more water) is often chosen when doses are tiny, so the mark on the syringe is not microscopic.
Measuring Your Dose on an Insulin Syringe
Insulin syringes are labeled in "units," not milliliters, which is where a peptide dosage calculator helps. On a U-100 syringe:
- 100 units = 1.0 mL (a full standard syringe)
- 50 units = 0.5 mL
- 10 units = 0.1 mL
So once you know the dose volume in mL, multiply by 100 to find the unit mark. Keep the concentration consistent across a vial so every dose lands on the same unit mark. Store the reconstituted vial refrigerated at roughly 2–8 °C, keep it away from light, avoid shaking (swirl gently to mix), and note that bacteriostatic water contains a preservative that extends usable life to around 28 days for many peptides — always follow the specific product and provider guidance.
Worked Example: 5 mg Vial + 2 mL BAC Water
Suppose you have a 5 mg peptide vial and add 2 mL of bacteriostatic water.
- Concentration = 5 mg ÷ 2 mL = 2.5 mg/mL (2,500 mcg/mL)
- For a 250 mcg dose: 250 mcg ÷ 2,500 mcg/mL = 0.1 mL
- Units to draw = 0.1 mL × 100 = 10 units on a U-100 insulin syringe
- Doses per vial = 5 mg ÷ 0.25 mg = 20 doses
So a 250 mcg dose is the 10-unit mark, and the vial provides 20 such doses. If you instead added 1 mL of water, the concentration would double to 5 mg/mL, the same 250 mcg dose would be only 5 units, and each mark would represent twice as much peptide.
Frequently Asked Questions
How many units is 250 mcg on an insulin syringe?
It depends on concentration. With a 5 mg vial reconstituted in 2 mL of BAC water (2.5 mg/mL), a 250 mcg dose equals 0.1 mL, which is 10 units on a U-100 insulin syringe. Halving the water to 1 mL doubles the concentration, making the same 250 mcg dose just 5 units.
How much bacteriostatic water do I add to a peptide vial?
There is no single required amount — you choose the volume to set a convenient concentration. Common choices are 1, 2, or 3 mL per vial. More water spreads the peptide across more units, making small doses easier to measure precisely. The peptide amount injected stays the same regardless of how much water you add.
How do I calculate peptide concentration after mixing?
Divide the milligrams of peptide in the vial by the milliliters of bacteriostatic water you added. For example, a 10 mg vial mixed with 2 mL of water gives 5 mg/mL, or 5,000 mcg/mL. This concentration is what converts your target dose into a volume and then into syringe units.
How many doses are in a peptide vial?
Divide the total peptide (mg) by the dose (mg). A 5 mg vial dosed at 250 mcg (0.25 mg) yields 5 ÷ 0.25 = 20 doses. The amount of bacteriostatic water does not change the number of doses — only the total peptide and the dose size do.
How long does reconstituted peptide last?
Once mixed with bacteriostatic water and refrigerated at about 2–8 °C, many peptides remain usable for roughly 28 days because the preservative limits bacterial growth. Storage life varies by peptide, so keep it cold, protect it from light, and follow the specific product and provider instructions. This tool does not provide medical advice.