Compounded GLP-1 Unit ↔ mg Converter

Why this tool exists

Patients on compounded semaglutide and tirzepatide are consistently asked by their telehealth provider to draw a dose in insulin syringe units rather than in milligrams — for example, “draw to the 40 unit mark.” The provider almost never explains where that number comes from, and patients then search Google for questions like “how many mg is 40 units of semaglutide?” to verify it. The answer depends on a single critical number that the provider should have mentioned but usually didn't: the concentration of the vial in milligrams per milliliter (mg/mL).

This converter is the math your prescriber should have shown you. Pick your drug, pick your vial concentration, and either enter the dose in milligrams to get the syringe units, or enter the units to get the milligrams. Common doses and common unit values are pre-populated in the lookup tables below the calculator.

The math (so you can verify it yourself)

The standard insulin syringe used worldwide is called a U-100 syringe, which means it is calibrated so that 100 units = 1 mL. This is the syringe almost always shipped by US compounding pharmacies with compounded GLP-1 vials [5, 6]. From there, the conversion is straightforward arithmetic:

units = (dose in mg × 100) ÷ concentration in mg/mL

mg = (units × concentration in mg/mL) ÷ 100

For example, if your prescriber gave you a 2.5 mg/mL vial of compounded semaglutide and asked you to start at 0.25 mg per week, the calculation is:

units = (0.25 × 100) ÷ 2.5 = 10 units

So you would draw the syringe to the 10-unit mark.

Common compounded concentrations

US compounding pharmacies dispense semaglutide and tirzepatide at a small number of standard concentrations. The two most common for each drug, as documented across the US compounded GLP-1 telehealth market we track:

• Semaglutide: 2.5 mg/mL or 5 mg/mL. The 2.5 mg/mL concentration is the most common; some 503A pharmacies dispense 5 mg/mL for higher-dose patients to keep the syringe volume manageable.
• Tirzepatide: 5 mg/mL or 10 mg/mL. The 10 mg/mL concentration is the most common because the Zepbound maintenance dose (15 mg weekly) would otherwise require drawing more than 1 mL on a single syringe.

The calculator above lets you switch concentration with a single click and recalculates everything live. Always confirm the actual concentration on your vial label before relying on any of the numbers below.

What can go wrong

The single most common patient error in compounded GLP-1 dosing is using the unit number from a friend or a previous vial that had a different concentration. Because the same number of units delivers a different milligram dose at each concentration, an unrecognized concentration change can produce a 2× under- or over-dose with no visible warning. A few specific things to watch:

1. The vial concentration changed. If your new vial label says 5 mg/mL and your old one said 2.5 mg/mL, your previous unit count will deliver double the milligrams. Recalculate before drawing.
2. The pharmacy changed. Different compounding pharmacies often use different default concentrations even when fulfilling the same prescription. Confirm the concentration with the new pharmacy.
3. The syringe is not U-100. Standard insulin syringes shipped with compounded GLP-1s are U-100. If you happen to use a U-40 or U-500 syringe (rare, but possible if you have leftover veterinary or insulin supplies), the calculation is different. Read the syringe label.
4. The dose exceeds 100 units (1 mL). If your calculated dose is more than 100 units, you cannot draw it on a single insulin syringe. You will need to either split into two injections, request a higher- concentration vial from the pharmacy, or use a tuberculin syringe (1 mL). Confirm with your prescriber.

Important safety disclaimer

This tool reports calculations only. The clinical safety checks (right vial, right concentration, right syringe, right patient, right time) are the prescriber's and the patient's responsibility. Weight Loss Rankings does not provide medical advice, diagnosis, or treatment recommendations. If you are unsure about your dose, do not inject. Call your prescriber or your compounding pharmacy and verify before you draw.

Related tools and research

• GLP-1 dose plotter: visualize how each titration step builds toward steady state in plasma.
• Compounded semaglutide bioequivalence: what 503A and 503B pharmacies are required to test, and where the real quality risks live.
• PCAB accreditation investigation: how to evaluate the pharmacy fulfilling your prescription.
• FDA warning letters database: cross-check your provider against documented enforcement actions.
• GLP-1 compounded pricing index: the live pricing snapshot for the entire compounded telehealth market.