How to use the dose unit converter

The converter above answers one question: for the dose on your prescription and the concentration on your vial, how much do you draw into the syringe? It gives the answer in millilitres and in U-100 syringe units, because those are the two scales you will actually see on the barrel.

What to type

Concentration. Read it off the pharmacy label on the vial itself, not from an email or an old vial. It is written one of two ways: as a rate, such as 10 mg/mL, or as a total, such as "10 mg in 1 mL" or "5 mg/2 mL". The converter has a toggle for each. If the label gives totals, use the second mode and type both numbers; the converter divides them for you and shows the rate it used.

Dose. Type the amount exactly as prescribed, then pick the unit it was written in. Most prescriptions for semaglutide and tirzepatide are in milligrams. Some pharmacies add a units figure to the label; that is a convenience translation for one specific concentration, and it stops being correct the moment the concentration changes.

What comes back

• Volume to draw, in mL. This is the physical amount.
• Units on a U-100 insulin syringe. Standard insulin syringes are graduated so that 100 units span 1 mL. The converter multiplies the volume by 100. If your syringe is not a U-100 insulin syringe, ignore this figure.
• Drug amount in mg and mcg, so you can confirm the milligram dose survived the conversion. If you entered a dose in mL or units, this is where you check it matches the prescription.
• Nearest syringe marks. Three common insulin syringes, with the exact result rounded to each one's smallest graduation and the rounding error shown. Syringes too small for the volume are struck out.

The two checks

Check one: does the mg figure match the prescription? Whatever unit you typed in, the mg line must equal what the prescriber wrote. If it does not, one of your inputs is wrong.

Check two: is the volume plausible for the syringe? Weekly GLP-1 doses from compounded vials are usually well under 1 mL. A result near or above 100 units means either the concentration is lower than you think or the dose was entered in the wrong unit. The FDA has published reports of people taking several times the intended dose of compounded semaglutide after confusing units with millilitres or milligrams. That is exactly the failure this check exists to stop.

Worked example

A vial labelled 10 mg/mL, a prescribed dose of 2.5 mg.

• Volume: 2.5 divided by 10 = 0.25 mL.
• Syringe units: 0.25 times 100 = 25 units.
• On a 0.3 mL syringe with half-unit marks: 25 units exactly. On a 1 mL syringe with 2-unit marks: 25 sits between 24 and 26, so the table shows 26 with a plus 1 unit error, and you would want the smaller syringe.

Next month's vial arrives at 5 mg/mL. The dose is still 2.5 mg. The volume is now 0.5 mL, or 50 units. Someone who kept drawing 25 units would take half the prescribed dose; someone with the reverse change would take double. This is why the converter asks for the concentration every time and never remembers it.

What the converter does not do

It does not check whether the dose is appropriate, whether it matches your titration step, or whether the product is what the label says. It is arithmetic. Compounded semaglutide and tirzepatide are not FDA approved, and the concentration on the vial is the pharmacy's statement, not a verified one. The reading a vial label guide covers how to check the label itself, and the FormBlends tirzepatide introduction covers the medication rather than the maths.