Semaglutide & tirzepatide reconstitution calculator
The reconstitution math is one line of arithmetic. Where most users go wrong is the units, not the formula. Worked examples for compounded semaglutide and tirzepatide.
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Verified May 10, 2026: Reconstitution is a single calculation, but the units make it feel hard. Once you understand what a U-100 syringe actually measures, the math collapses to one line. This page covers the formula, two worked examples (one semaglutide, one tirzepatide), and the most common error.
The one-line formula
Or, equivalently:
Worked example: 5 mg semaglutide vial, 0.25 mg dose
You have a 5 mg vial. You add 1 mL of BAC water. Your concentration is 5 mg/mL. Your starter dose is 0.25 mg.
dose volume = 0.25 mg ÷ 5 mg/mL = 0.05 mL
On a U-100 insulin syringe, 0.05 mL = 5 units.
If you instead added 2 mL of BAC water, your concentration would be 2.5 mg/mL. Your dose volume would double to 0.1 mL = 10 units. Same dose, different volume.
Worked example: 30 mg tirzepatide vial, 5 mg dose
You have a 30 mg vial reconstituted in 2 mL BAC water. Concentration is 15 mg/mL. Your dose is 5 mg.
dose volume = 5 mg ÷ 15 mg/mL = 0.33 mL
That's 33 units on a U-100 syringe.
If the pharmacy reconstitutes the same vial in 1 mL, concentration jumps to 30 mg/mL and the dose volume drops to 0.166 mL = 17 units. The dose is the same. The volume is half.
The U-100 syringe trap
A U-100 insulin syringe is graduated in units, where:
This was designed for U-100 insulin (where 1 unit of insulin = 0.01 mL of liquid = 1 unit of insulin activity). For peptides, the units are just a volume marking. Forgetting this and treating "units" as "milligrams" is the most common error in compounded GLP-1 dosing.
Why dose volume changes when BAC water changes
Your prescriber writes you a dose in milligrams. The pharmacy reconstitutes the vial in some volume of BAC water. Your dose volume is a function of both.
Concretely: if you're stable on 25 units of compounded semaglutide and the pharmacy switches from 1 mL to 2 mL BAC water on your next refill, you need to draw 50 units to get the same dose. If you keep drawing 25, you've cut your dose in half.
This happens. Pharmacies change protocols, ship sizes, or reconstitution standards without flagging the change. Read the instructions on every refill.
How Titrate eliminates this entirely
Punch in three numbers — vial mg, BAC water volume, target dose — and Titrate's reconstitution calculator returns the syringe units to draw. The formula is shown beneath the result, so you can verify the math by hand the first few times.
When the pharmacy changes concentrations, you change the vial mg or BAC volume input and the output recalculates. No spreadsheet, no half-remembered ratio.
Frequently asked questions
What is BAC water?
Bacteriostatic water — sterile water with 0.9% benzyl alcohol added as a preservative. The benzyl alcohol prevents bacterial growth in the vial after the rubber stopper has been punctured. Use only BAC water for peptide reconstitution; sterile water without preservative spoils faster.
What's a U-100 syringe?
An insulin syringe graduated in 100 units per mL. 1 unit = 0.01 mL. The graduations make it easy to draw small volumes accurately. U-40 syringes also exist for veterinary insulin but are not interchangeable for peptide dosing.
What if my dose volume is more than 1 mL?
U-100 insulin syringes typically max at 1 mL (100 units). If your prescribed dose volume exceeds this, your pharmacy is using a low-concentration formulation. Either request a higher-concentration vial or split the dose into two injections (less common but accepted).
Can I reuse a U-100 syringe?
No. Single-use only, both for sterility and to prevent dose miscalculation from residual liquid in the syringe.
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider before starting, modifying, or stopping any medication or peptide protocol. Information is current as of the publication date and may change.