Units to mg converter, for peptides

How the math works

Units are volume: the number printed on an insulin syringe counts fractions of a milliliter, and nothing else. Which fraction it counts depends on the barrel, which is why the scale sits in the form above as an input rather than as a detail.

Milligrams are mass: the vial label states how much peptide arrived in the vial, and a barrel graduated in units is reporting volume, so that figure is not on the syringe. The two systems only meet through the water.

Concentration is the bridge: vial milligrams divided by water milliliters gives mg per mL, and mg per mL divided by the syringe's units per mL gives the milligrams inside a single unit. A 20mg vial with 2mL of water comes out to 10mg per mL, so one U-100 unit holds 0.1mg, or 100mcg.

One equation, both directions: milligrams divided by the per-unit value lands on the unit mark, and a unit mark multiplied by the per-unit value lands back on the milligrams. Every step after the scale is that division, redoable by hand. The scale itself is not: that a U-100 barrel carries 100 units in a milliliter and a U-40 carries 40 is a device and label fact, and both labels are cited below.

One worked example

The labeled example: a 20mg vial, 2mL of bacteriostatic water, and a U-100 syringe. Every figure below is arithmetic on those three choices, not a chart for any particular vial in anyone's hands.

How many units is 1mg?

There is no fixed number, because units measure volume and milligrams measure mass, and only the concentration connects them. At 10mg per mL (a 20mg vial plus 2mL of water), 1mg reads as 10 units on a U-100 syringe; at 5mg per mL the same 1mg reads as 20 units.

What is the difference between U-100 and U-40?

The barrel scale. U-100 packs 100 units into each mL, so one unit is 0.01mL; U-40 packs 40 units into each mL, so one unit is 0.025mL, two and a half times the liquid per mark. The scale sets volume only, and the milligrams at any mark still come from the vial and the water.

Why does my answer differ from the chart?

Because every chart carries its own vial size, water amount, and syringe scale, and a chart that leaves any of the three unstated cannot be reconciled with one that states them. A 2.5mg amount is 25 units at 10mg per mL and 50 units at 5mg per mL. Match all three assumptions and the numbers agree; miss any one and they never will.

How many mL is 50 units?

On a U-100 syringe, 50 units is 0.5mL. Counted on a U-40 scale, where one unit is 0.025mL, fifty units works out to 1.25mL, more liquid than a 1mL barrel holds. A unit count is a volume reading and never a mass, so the milligrams sitting inside that volume only exist once the concentration is known.

More dose math

The rest of the cluster: this converter is one tool in the dose-math library we maintain. The neighboring pages:

• The peptide dose math index: every dose-math page and tool, collected in one place.
• Reconstitution calculator: vial plus water to concentration, then the draw volume for any milligram figure you bring to it.
• Bacteriostatic water calculator: works the bridge equation backwards, from a vial and a chosen concentration to the water volume.
• Concentration vs dose: the explainer behind the wrong unit counts this converter exists to prevent.
• Tirzepatide dosage guide: this same units math inside a full compound reference, with the trial record attached.
• The embeddable version: this converter as a widget any other site can host with one line, free, with an attribution link back.

How this page is sourced

Arithmetic, with one exception: every figure the converter returns, and every row of the worked example, is multiplication or division that can be redone by hand from the inputs printed beside it.

The exception, and the tool rests on it: the two barrel scales. That a U-100 barrel carries 100 units in a milliliter and a U-40 carries 40 is a device and label fact, not something arithmetic can produce, so an approved label for each scale is cited below.

What changed on 30 July 2026: a citation audit found this page claiming there was nothing on it to cite, which was false, and describing a U-40 barrel as carrying the same 50-unit mark as a U-100. The scale facts now carry their labels, and the 50-unit answer is stated as a count on the U-40 scale rather than as a mark on a U-40 barrel, because a 1mL U-40 barrel holds 40 units and this site holds no document specifying which marks a given syringe prints.

Two sources: two approved prescribing informations, both read on DailyMed.

The standard: the sourcing and citation-verification standard for the site lives on the methodology page, including who checks a page before it ships.

1. 1

   Humalog (insulin lispro) injection, for subcutaneous or intravenous use. Prescribing information, Eli Lilly and Company. Dosage Forms and Strengths, printing the strength as 100 units/mL (U-100); and the Principal Display Panel for the 10 mL vial, reading "Use only with a U-100 syringe". Retrieved 30 July 2026, HTTP 200. DailyMed SPL, set id c8ecbd7a-0e22-4fc7-a503-faa58c1b6f3f.

2. 2

   Vetsulin (porcine insulin zinc suspension) injection. Label, Merck Sharp & Dohme Corp. Description and How Supplied, giving 40 IU/mL; the client information sheet, stating that U-40 insulin contains 40 units/mL; and Dosage and Administration, stating that use of a syringe other than a U-40 syringe will result in incorrect dosing. Retrieved 30 July 2026, HTTP 200. DailyMed SPL, set id 4472644f-edc1-4a4f-8506-888bd8ad895a.