Insulin Syringe Units Explained: 1 mL Is How Many Units on a U-100 Syringe?

The rule never changes on a U-100 syringe: units divided by 100 is mL, and mL times 100 is units.

Insulin syringes were designed for insulin, which is measured in units of activity. The standard insulin strength in the US is U-100, meaning 100 units of insulin in each millilitre, and U-100 syringes are marked so that each line equals one unit of U-100 insulin. Because the insulin concentration is fixed, the markings work out to a fixed volume: 1 unit is 0.01 mL.

When the same syringe is used for anything that is not U-100 insulin, such as a compounded peptide or a GLP-1 vial, the unit marks are simply a volume scale. 25 units means 0.25 mL of whatever is in the vial, nothing more.

Syringes marked for other insulin concentrations exist. The conversion on this page applies only to syringes labelled U-100, which is what Pepti ships with its injectables.

U-100 syringes come in several barrel sizes. A unit is the same volume on all of them; what changes is how much the barrel holds and how far apart the lines are.

Check the markings on the syringe you have rather than assuming. On a barrel marked every 2 units, an odd number such as 25 sits halfway between two lines. Trouble comes from switching barrel size mid-prescription and reading the new one from habit rather than by number. A direction larger than your barrel, such as 68 units in a 50-unit syringe, is not something to solve with two draws: message your care team.

Some directions exceed a 1 mL barrel altogether. Pepti's methylcobalamin, for example, is directed at 1.25 mL (125 units) intramuscularly once weekly, and is supplied with an appropriate syringe, usually marked in millilitres.

This is the single most important idea on the page. Two people drawing 25 units of different medications, or of the same medication at different concentrations, are drawing the same volume and very different amounts of drug.

Turning units into milligrams

Two steps:

1. Units divided by 100 gives mL.
2. mL times the vial's concentration (mg/mL) gives mg.

This is arithmetic, labelled as such: a sanity check on a label, not a way to set a dose. If your label says 1 mg/mL, your directions say 0.25 mL, and someone tells you that you are taking 2.5 mg, one of you is wrong, and it is worth a message to your care team.

Real examples from Pepti directions

Every price is all-in: medication, physician review, refill management and shipping, with no membership fee. Your own directions are the ones printed on your vial. GLP-1 conversions are covered in detail in tirzepatide units to mg and semaglutide units to mg.

• Hold it vertical, at eye level. Reading at an angle biases every dose in the same direction.
• Read the flat front edge of the rubber plunger tip, the edge nearest the needle, against the marking, not the raised ring behind it.
• Clear large bubbles. If 3 of your 25 units are a bubble, you have drawn 22 units of medication. Tap the barrel, push the bubble back into the vial, and redraw.
• Say the number out loud in units as you draw.
• Never round to an easier mark. If your direction is 18 units, 20 is not close enough.

The ten-fold error

The mistake that matters most is converting in the wrong direction: reading 0.25 mL and drawing to the 2.5 mark, a ten-fold error, or reading 25 units and drawing a quarter of a barrel that holds only 0.3 mL. The FDA's July 2024 alert on compounded semaglutide described patients given U-100 syringes and asked to measure small doses in units drawing five to twenty times the intended amount. If your directions and syringe markings seem to disagree, do not inject; message your care team. If you have already injected more than directed, call Poison Control at 1-800-222-1222, call 911 for severe symptoms, and see GLP-1 overdose.

Insulin syringes have a fixed needle. Two numbers describe it:

The international injection technique recommendations from the Forum for Injection Technique and Therapy (FITTER), published in Mayo Clinic Proceedings in 2016, concluded that the shortest needles, 4 mm on a pen and 6 mm on a syringe, should be first-line for subcutaneous injection, and that intramuscular injection should be avoided where subcutaneous was intended. Use a new syringe every time; reuse blunts and burrs the tip.

The units-to-mL conversion is a fixed standard, not a matter of evidence. What the evidence does show is that the conversion is where serious errors happen: the FDA has documented adverse events, some requiring hospitalization, from people measuring incorrect doses from compounded vials with insulin syringes, and from clinicians miscalculating between milligrams, units and millilitres. The injection technique advice here comes from the insulin literature, the largest body of self-injection experience there is. None of it sets a dose. Compounded medications are not FDA approved, and the concentration on your label, together with the direction your physician wrote, is what turns a unit mark into a dose. The full technique is in how to inject peptides safely, and doses per vial in how long does a peptide vial last.

1. Complete a free online intake covering your history, medications and what you want help with.
2. A physician licensed in your state reviews it, usually within 24 hours.
3. If it is appropriate, a PCAB-accredited, FDA-registered US 503A pharmacy compounds it, shipped as a multi-dose solution ready to use, with directions printed on the vial in both mL and units.
4. It ships refrigerated with ice packs, sterile U-100 syringes and alcohol prep pads.
5. Your care team stays reachable for questions, and refills run every 28 days, one vial per fill.

Pepti is cash-pay and does not bill insurance. Bloodwork is not required for any Pepti treatment. If your physician wants labs for your care, they'll ask through your account. Lot test results are published at /quality/lab-results. Step-by-step pages: tirzepatide, semaglutide, BPC-157, tesamorelin and NAD+.