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Free tool · math only
Peptide reconstitution calculator: mg, mcg, mL & units
Any vial, any peptide. Enter the mg in the vial, the water added and the amount you want to measure. Get the concentration, the mL and the U-100 syringe units instantly, with every step of the math shown.
Your concentration, volume and units will show here.
Math only. This tool never suggests a dose, and it has no presets: every number comes from you. It's for U-100 insulin syringes only (100 units = 1 mL). On a prescription? Follow your prescriber and pharmacist and double-check with them.
Not sure if your vial is compounded or brand-name? Here's how to tell in two minutes.
The math, plainly
- Concentration (mg/mL) = mg in the vial ÷ mL of water added. Multiply by 1,000 for mcg/mL. If your label already says mg/mL, use that.
- mL to measure = amount in mg ÷ concentration. (Amount in mcg? Divide by 1,000 first.)
- Units on a U-100 syringe = mL × 100.
Three steps. Concentration is the one that changes everything: add more water and the same amount becomes more units.
Why people mix these up
Milligrams (mg) and micrograms (mcg) measure the peptide. Milliliters (mL) and syringe "units" measure liquid. The FDA has received reports of dosing errors with compounded semaglutide where people confused mg, mL and units, including patients told to draw 5 units (0.05 mL) on a U-100 syringe who drew 50 units instead. FDA says compounded concentrations can vary, even from one compounder.
On a GLP-1? Read the semaglutide guide and the tirzepatide guide for label dosing straight from the FDA. Exploring other peptides? Browse all our peptide guides, and see how to tell if a source is legit.
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Peptide calculator FAQ
How do I calculate peptide concentration after reconstitution?
Divide the mg in the vial by the mL of water added. A 10 mg vial with 2 mL added is 5 mg/mL, which is 5,000 mcg per mL. That number drives everything else.
How many units is 1 mL on an insulin syringe?
On a U-100 insulin syringe, 1 mL is 100 units, so 0.1 mL is 10 units and 0.01 mL is 1 unit. 'Units' on the syringe are a measure of volume, not of drug.
How do I convert mcg to units?
Convert mcg to mg (divide by 1,000), divide by the concentration in mg per mL to get mL, then multiply by 100 for U-100 syringe units. The calculator shows every step.
Why does the same amount come out to different units?
Because concentration changes with how much water goes in. The same amount is fewer units in a stronger vial and more units in a weaker one. FDA notes that compounded semaglutide can come in different concentrations, even from the same compounder.
Does this calculator tell me what dose to take?
No. It only does the math on the numbers you enter. It never suggests a dose, and it has no presets. For prescription drugs, follow your prescriber and pharmacist and double-check with them.
Sources: FDA alert on compounded semaglutide dosing errors; FDA's concerns with unapproved GLP-1 drugs.
Not medical advice. Education only. Talk to a licensed clinician about your health.