Peptides calculator
To dose a reconstituted peptide, divide vial strength in mg by diluent volume in mL to get concentration, then divide your dose by that and multiply by 100 for units on a U-100 insulin syringe. A 5 mg vial in 2 mL gives 2.5 mg/mL, so 250 mcg is 10 units.
The three numbers every peptide calculation needs
Vial strength in milligrams, diluent volume in milliliters, and intended dose. Everything else follows. Strength divided by volume gives concentration in mg per mL; dose divided by concentration gives volume in mL; volume multiplied by 100 gives units on a U-100 insulin syringe.
Nearly every dosing error traces back to one of two things: mixing micrograms and milligrams in the same calculation, or reconstituting with a different volume than the one used for the math. Write the diluent volume on the vial the moment you add it.
- Concentration (mg/mL) = vial strength (mg) ÷ diluent (mL).
- Convert your dose to the same unit as the concentration — 250 mcg is 0.25 mg.
- Volume (mL) = dose (mg) ÷ concentration (mg/mL).
- Units on a U-100 syringe = volume (mL) × 100.
- Doses per vial = vial strength ÷ dose, in matching units.
Common reconstitution results at a glance
Read down the row you actually used. Halving the water doubles the concentration and halves the units for the same dose — which is exactly how an accidental double dose happens.
| Vial | Bacteriostatic water | Concentration | 250 mcg | 500 mcg |
|---|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 5 units | 10 units |
| 5 mg | 2 mL | 2.5 mg/mL | 10 units | 20 units |
| 5 mg | 3 mL | 1.67 mg/mL | 15 units | 30 units |
| 10 mg | 2 mL | 5 mg/mL | 5 units | 10 units |
| 10 mg | 5 mL | 2 mg/mL | 12.5 units | 25 units |
Mistakes the calculator cannot catch
- Using a U-40 or U-50 syringe while calculating for U-100. Check the barrel marking before you draw.
- Assuming the vendor's stated strength is correct. Without a batch certificate of analysis, the mg figure is unverified.
- Forgetting syringe dead space, which quietly costs you the last partial dose in a vial.
- Reconstituting with sterile rather than bacteriostatic water for a vial you will use over multiple days.
- Losing track of the reconstitution date, so the beyond-use date becomes a guess.
- Shaking the vial. Swirl gently; foaming denatures peptide at the air–liquid interface.
Run the numbers
The one interactive tool: mix the vial, convert any dose to U-100 or U-40 units, and see how long the vial lasts.
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Frequently asked questions
- How do you calculate a peptide dose?
- Divide the vial strength in mg by the diluent volume in mL to get the concentration. Divide your intended dose by that concentration, then multiply by 100 to get units on a U-100 insulin syringe. A 5 mg vial in 2 mL is 2.5 mg/mL, so a 250 mcg dose is 10 units.
- How many units is 250 mcg of a peptide?
- It depends entirely on the concentration. With a 5 mg vial reconstituted in 2 mL, 250 mcg is 10 units on a U-100 syringe. With the same vial in 1 mL, the same 250 mcg is only 5 units. The units figure is meaningless without the diluent volume.
- How much bacteriostatic water should I add?
- Choose a volume that puts your usual dose between roughly 10 and 30 units, which is the easiest range to read accurately. More diluent makes small doses easier to measure; less diluent means fewer injections' worth of volume but harder-to-read markings.
- Is 100 units the same as 1 mL?
- On a U-100 insulin syringe, yes: 100 units equals 1 mL, so each unit is 0.01 mL. This is a volume marking, not a dose of peptide, which is why the concentration has to be worked out first.
- How many doses are in a vial?
- Divide the total vial strength by your dose, keeping the units consistent. A 10 mg vial at 500 mcg per dose is 10,000 mcg ÷ 500 mcg, or 20 doses — assuming none is lost to dead space in the syringe or to expiry before you finish it.
- Does the calculator work for tirzepatide and semaglutide?
- The same reconstitution math applies to any lyophilized peptide sold in mg. Prescribed pens are pre-filled and dose-marked by the manufacturer, so you should follow the pen's markings and your prescriber's instructions rather than calculating anything.
References & evidence
Sources cited on this page. Last reviewed August 2026. Corrections: editorial policy.
- US Food and Drug Administration. Insulin Syringes and Needles — dose accuracy and U-100 markings. https://www.fda.gov/drugs/emergency-preparedness-drugs/information-regarding-insulin-storage-and-switching-between-products-emergency
- Institute for Safe Medication Practices. ISMP List of Error-Prone Abbreviations, Symbols, and Dose Designations. https://www.ismp.org/recommendations/error-prone-abbreviations-list
- US Pharmacopeia. General Chapter <797> Pharmaceutical Compounding — Sterile Preparations (beyond-use dating principles). https://www.usp.org/compounding/general-chapter-797
- US Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding — Category 2 list. https://www.fda.gov/drugs/human-drug-compounding/bulk-drug-substances-used-compounding-under-section-503a-fdc-act
Stop recalculating every injection
Save each vial once — strength, diluent, reconstitution date — and DoseRoutine shows the syringe units for every scheduled dose, counts down what's left in the vial, and rotates your injection sites.
Start free in DoseRoutineEducational reference only, not medical advice. Talk to a qualified clinician before starting, stopping or combining any peptide, supplement or medication.