Reverse Dose Calculator
Find the milligrams represented by a U-100 syringe marking using the concentration printed on your prescribed liquid vial. Enter both values below to see the arithmetic.
- 1Enter U-100 units
- 2Enter vial mg/mL
- 3See calculated mg
A QUICK WALKTHROUGH
How this reverse dose calculator works
The tool converts a U-100 volume marking to milligrams using the concentration you supply. It does not know the contents of your vial.
Check the syringe scale
Confirm that the syringe is U-100. Enter its marking number, which represents volume rather than drug strength.
Read the vial concentration
Enter the mg/mL printed on the same liquid vial. Different vials can have different concentrations.
Convert units to volume
Divide U-100 markings by 100 to get milliliters. Twenty markings, for example, are 0.2 mL.
Calculate the equivalent mg
Multiply the volume by mg/mL. Check the result against your written prescription with your pharmacist or prescriber.
Reverse dose formula: syringe units to mg
Milligrams = (U-100 syringe units ÷ 100) × vial concentration (mg/mL). The first part gives liquid volume in mL. Multiplying by the specific vial concentration converts that volume to a calculated medication amount. The reverse calculation cannot work from units alone because units describe volume, not drug mass.
Examples with different vial concentrations
For 20 U-100 markings, the volume is 0.2 mL. If a hypothetical vial label says 2 mg/mL, the calculation is 0.2 × 2 = 0.4 mg. If the label instead says 5 mg/mL, the same 20 markings calculate to 1 mg. These are arithmetic illustrations, not dose recommendations. Use only the exact concentration from your own vial.
If your label clearly gives a total amount and total volume, dividing total mg by total mL gives mg/mL. For example, 5 mg in 2 mL is 2.5 mg/mL. If the label instead says mg per dose, or the meaning of either number is unclear, ask the dispensing pharmacist before using the calculator.
When the result is not safe to use
Do not use this tool for a branded GLP-1 pen, tablet, prefilled syringe, an unknown vial concentration or a non-U-100 syringe. It cannot check product authenticity, sterility, the actual concentration, your prescribed dose or whether a compounded medication is appropriate. It also does not provide injection instructions.
The FDA reports serious overdoses from compounded injectable semaglutide dosing errors, including confusion between milligrams, milliliters and syringe units. The FDA also describes concerns with unapproved GLP-1 products. If the label and prescription do not clearly agree, stop and contact your pharmacist or prescriber. This page provides educational arithmetic only, not medical advice.
Reverse Dose Calculator FAQs
How do I convert U-100 syringe units to mg?
Divide the U-100 marking by 100 to find mL, then multiply by the concentration on your vial label in mg/mL. The result depends on that specific concentration. This calculation does not select a dose.
How many mg is 10 units on a U-100 syringe?
Ten U-100 markings represent 0.1 mL, but there is no fixed mg amount. At a hypothetical 2 mg/mL, 0.1 mL contains 0.2 mg. At 5 mg/mL, it contains 0.5 mg. Check the exact vial label with your pharmacist.
How many mg is 20 units on a U-100 syringe?
Twenty U-100 markings represent 0.2 mL. Multiply 0.2 by the concentration in mg/mL on the specific vial label. For example, 0.2 mL at a hypothetical 2 mg/mL is 0.4 mg, not a recommended amount.
How many mg is 50 units on a U-100 syringe?
Fifty U-100 markings represent 0.5 mL. The mg amount equals 0.5 times the vial concentration in mg/mL. For example, a hypothetical 2 mg/mL concentration gives 1 mg.
Can I use this for compounded semaglutide or tirzepatide?
The arithmetic can describe a prescribed liquid vial only when its actual concentration is known in mg/mL and the syringe is U-100. The tool cannot confirm vial contents, product suitability, legal status or your prescribed dose. Ask your pharmacist or prescriber to verify the instructions.
Can I use this for Ozempic, Wegovy, Mounjaro or Zepbound pens?
No. Pen doses are set using product-specific device instructions. This calculator converts U-100 syringe volume markings for a liquid vial, not pen clicks, dial settings, tablets or prefilled syringes.
What if my label lists total mg and total mL?
If both values clearly refer to the same solution, total mg divided by total mL gives mg/mL. For example, 5 mg in 2 mL is 2.5 mg/mL. If the label is ambiguous or gives mg per dose, do not guess: confirm the concentration with the dispensing pharmacist.
Is 1 unit always 0.01 mL?
Only on a U-100 syringe scale. One U-100 marking corresponds to 0.01 mL of volume. It does not correspond to a fixed number of milligrams and this calculator is not for U-40 or other scales.
Does this result tell me how much to inject?
No. It only converts the numbers entered. It cannot verify a prescription or account for a different vial concentration or syringe type. FDA has reported serious dosing errors when people confused units, mL and mg. Confirm the intended measurement with a healthcare professional before injection.
Sources
Sources checked . Calculations are not a prescribed dose or confirmation of vial contents. Talk to your healthcare professional before changing how you take medication.