Semaglutide Hub

Calculator

Vial units to mg converter

Enter the concentration printed on a compounded semaglutide vial and the dose your prescriber wrote. Get the volume, the U-100 syringe units, the nearest mark on each syringe size with its rounding error, and how many full doses the vial holds.

By FormBlends editorial teamAssumptions checked September 4, 2026 Runs in your browser; nothing is sent to a server

What it computes

Compounded vial concentration to mL, syringe units and the nearest mark.

Never pre-fills a dose

Inputs

Compounded semaglutide vials state either a total (for example 5 mg in 2 mL) or a concentration (2.5 mg/mL). Copy it exactly from the pharmacy label.

mg
mL

Enter the number written on your prescription. Nothing is pre-filled; this tool never suggests a dose.

Result

Enter the concentration and the prescribed dose. The volume, syringe units and nearest syringe mark appear here.

Formula
concentration (mg/mL) = total mg in vial / total mL in vial
volume (mL)           = dose (mg) / concentration (mg/mL)
U-100 units           = volume (mL) x 100
dose from units (mg)  = units / 100 x concentration
nearest mark          = round(units / mark size) x mark size     (0.5, 1 or 2 units by syringe)
rounding error (%)    = (delivered mg - prescribed mg) / prescribed mg x 100
full doses in vial    = floor(total mg / dose mg)

Units on an insulin syringe measure volume: 100 units per 1 mL. The tool treats them that way and never as an amount of drug. The mark sizes come from the three common U-100 syringe sizes.

Assumptions, checked September 4, 2026
  • U-100 syringes only: 0.3 mL (half-unit marks), 0.5 mL (1-unit marks) and 1 mL (2-unit marks). If your syringe is different, read its smallest graduation and round by hand.
  • Rounding errors of 5% or more are flagged in red. A smaller syringe usually reduces the error; whether a given error matters is a question for your prescriber.
  • Brand pens (Ozempic, Wegovy) deliver a fixed dose per click or pen and are not measured in syringe units. This tool is for pharmacy-dispensed vials with a stated concentration.
  • Compounded semaglutide is not FDA approved. This tool is arithmetic for a dose a licensed prescriber wrote; it does not decide a dose.

This calculator is an arithmetic aid for medication a licensed prescriber has already prescribed. It does not recommend a dose. Confirm any result with your prescriber or pharmacist before use.

Sources

  1. ISMP Guidelines for Optimizing Safe Subcutaneous Insulin Use in Adults (U-100 syringe graduations)
  2. FDA: FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss (content current 2026-09-01)
  3. Wegovy (semaglutide) injection and tablets prescribing information, revised 6/2026, DailyMed set id ee06186f-2aa3-4990-a760-757579d8f77b

Read before you use it

Guides for this calculator

Paper-cut illustration of a syringe with plain tick marks beside a slide rule and a ruler

Compounded semaglutide units to mg: how the converter works

You'll get: A brand pen gives a fixed dose; a compounded vial makes you measure with a syringe, and that is where errors happen.

Why a compounded semaglutide vial needs arithmetic that a brand pen does not, how the converter turns a concentration and a prescribed dose into syringe units and the nearest mark, and the errors it is built to catch.

Updated September 4, 2026

Educational, not medical advice. Read the medical disclaimer.