Peptide dosing Calculator 2026 Reviewed and Tested: Addressing Reconstitution and Dosing Errors
Clinically Reviewd and tested by: Dr: Sameen Abbas Kazmi
Peptide Dosing Calculator
Units to draw = dose (mcg) ÷ [vial mg × 1000 ÷ water mL] × 100. Example: a 5 mg vial mixed with 2 mL of bacteriostatic water holds 2,500 mcg per mL, or 25 mcg per unit. A 250 mcg dose is 10 units (0.10 mL) on a U-100 insulin syringe. This tool converts a dose your prescriber already set. It does not choose a dose.
How do I convert mcg to units on an insulin syringe?
Divide your dose in mcg by the mcg per unit. Mcg per unit = vial mg × 10 ÷ water mL, because a U-100 syringe has 100 units per mL and 1 mg is 1,000 mcg. A 5 mg vial in 2 mL gives 25 mcg per unit, so 250 mcg ÷ 25 = 10 units. Here a “unit” is a volume mark on the syringe, not a measure of the drug, so it is not the same as the potency units used for insulin or hCG.
How is the concentration calculated?
Concentration (mg/mL) = vial mg ÷ water mL. The peptide spreads evenly through the liquid, so a 5 mg vial in 2 mL is 2.5 mg/mL. On a U-100 insulin syringe, 100 units equal 1 mL, so one unit is 0.01 mL.
- Units to draw = dose (mcg) ÷ (vial mg × 1000 ÷ water mL) × 100
- Doses per vial = vial mg × 1000 ÷ dose (mcg), rounded down
- Convert: 1 mg = 1,000 mcg
Does adding more water change my dose?
No. More water lowers the concentration, so the same dose takes more units. Less water raises it, so the dose takes fewer units. This table is our own calculation for a 5 mg vial:
How much water should I add? Any volume works mathematically. Choose the one that puts your dose on a clear, easy-to-read mark, and confirm it with your pharmacist or the product label. The optional field in the calculator works this out for you.
| Water | mg/mL | mcg per unit | 100 mcg | 250 mcg | 500 mcg |
|---|---|---|---|---|---|
| 1 mL | 5.00 | 50 | 2 | 5 | 10 |
| 2 mL | 2.50 | 25 | 4 | 10 | 20 |
| 3 mL | 1.67 | 16.7 | 6 | 15 | 30 |
| 4 mL | 1.25 | 12.5 | 8 | 20 | 40 |
| 5 mL | 1.00 | 10 | 10 | 25 | 50 |
Doses per vial at 100 / 250 / 500 mcg: 50 / 20 / 10. Water volume does not change this.
Which insulin syringe size should I use?
| Syringe | Capacity | Best for | Watch for |
|---|---|---|---|
| 1 mL | 100 units | Larger draws | Small doses sit on closely spaced marks (often every 2 units) |
| 0.5 mL | 50 units | Mid-size doses | Cannot hold more than 50 units |
| 0.3 mL | 30 units | Small doses | Marks are farther apart, so easier to read. Check your brand’s scale. |
All three use the same U-100 scale, so a given dose is the same number of units on each. A smaller barrel just makes small doses easier to read.
How common are dosing errors with vials and syringes?
The U.S. FDA reported overdoses from compounded semaglutide in which patients drew 5 to 20 times the intended dose from multi-dose vials, some needing hospitalization. In one example, a patient told to draw 5 units (0.05 mL) drew 50 units (0.5 mL). The FDA also reported clinicians miscalculating doses by 5 to 10 times, and pointed to confusion between mL, mg and “units” as a likely cause.1,2 Semaglutide is one drug, but the unit-versus-mL trap applies to any vial you draw by hand.
How do I reconstitute a peptide vial?
- Wash your hands. Wipe both vial stoppers with an alcohol swab and let them dry.
- Draw the exact water volume you used in the calculator.
- Inject the water slowly down the inside wall of the vial, not onto the powder.
- Swirl gently until clear. Do not shake. Do not use if cloudy or if particles remain.
- Write the mix date and water volume on the vial. Refrigerate unless the label says otherwise.
- Dispose of needles in a sharps container. Never share needles.
How long does a mixed vial last?
A common rule for preserved multi-dose vials is 28 days after first puncture, unless the product labeling says otherwise (USP <797>).4 Some peptides are stable for less time. Follow the label or your pharmacist. Do not assume 28 days applies to every peptide.
Are the peptides I’m using FDA-approved?
Not always. Some peptide drugs, such as semaglutide, are FDA-approved. Others sold as “research peptides” are not. The FDA keeps categorized lists of bulk substances for compounding, and the status of some peptides has changed in 2026.3 Check the current list before relying on any product. We do not list example doses for specific peptides because we cannot verify safe dosing for them.
How does this calculator compare with doing the math by hand?
| This calculator | By hand | Clinic or pharmacy | |
|---|---|---|---|
| Speed | Seconds | 2 to 5 minutes | Appointment or call |
| Catches impossible draws | Yes (syringe capacity, too-small units) | Only if you check | Yes |
| Sets your dose | No | No | Yes |
| Knows your health history | No | No | Yes |
Use the calculator to check arithmetic. Get the dose and technique from a licensed clinician.
FAQ
What if my result is not a whole number?
Round only to a mark you can read reliably (often 0.5 or 1 unit). If you land between marks every time, change the water volume or use a smaller syringe, after checking with your pharmacist.
Can I use sterile water instead of bacteriostatic water?
Follow the diluent your prescriber or the product label names. Sterile water has no preservative, so it is generally for single use.
What does the calculator not account for?
Syringe dead space, vial overfill and small volume changes when powder dissolves. Real doses per vial may be slightly fewer than shown.
How was this calculator checked?
The arithmetic follows the formulas shown above and matches the worked examples and tables on this page. We update the page when its sources change.
References
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