How many units is 1 mL on an insulin syringe?

On a U-100 syringe, 1 mL is 100 units, so one unit is 0.01 mL. On a U-40 syringe, 1 mL is 40 units, so one unit is 0.025 mL. Almost every syringe sold for human use is U-100.

What is the difference between a 0.3 mL, 0.5 mL and 1 mL insulin syringe?

Only the total capacity. All three are U-100, so a unit means the same volume on each. A 0.3 mL barrel holds 30 units, a 0.5 mL holds 50, a 1 mL holds 100. The smaller barrel spreads those units over the same physical length, which makes small doses easier to read accurately.

How do I know if my syringe is U-100 or U-40?

It is printed on the barrel or the wrapper. U-40 syringes are usually veterinary and often have a red plunger. If you use a U-40 syringe with numbers worked out for U-100 you will draw two and a half times the intended dose.

What does 20 units mean in mL?

On a U-100 syringe, 20 units is 0.2 mL. The mass of peptide in that 0.2 mL depends entirely on how concentrated your vial is.

How to read an insulin syringe

Units are not a dose. They are a volume. Everything below follows from that one fact.

Reviewed 3 September 2026
27 compounds
Formula on every page
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A unit is a volume, not an amount of drug

The numbers on an insulin syringe measure liquid, not medicine. On a U-100 syringe, which is what almost everything sold for human use is, 100 units is 1 mL. So one unit is 0.01 mL, twenty units is 0.2 mL, and fifty units is half a millilitre.

How much peptide is in that volume depends entirely on how concentrated your vial is, which is why nobody can answer "how many units should I take" without also knowing your vial strength and how much water you added.

The three sizes, drawn to scale

Here is the same 0.2 mL on all three common barrels. The liquid is identical in every row. Only the number you read changes, and only because the scale is stretched over a different length.

This is why a smaller barrel is better for a small dose. Twenty units occupies two thirds of a 0.3 mL syringe and one fifth of a 1 mL syringe, so the same misjudgement of a millimetre costs you far less on the small one.

The U-40 trap

A U-40 syringe holds 40 units in 1 mL, not 100. If you take a unit count worked out for a U-100 syringe and draw it on a U-40 barrel, you will take two and a half times what you intended. U-40 syringes are usually veterinary and often have a red plunger. Check the barrel before every draw.

Reading it accurately

Read at eye level, with the syringe vertical. Looking down at an angle shifts the apparent line.
Read the edge of the plunger stopper that faces the needle, not the middle of the rubber.
Flick out air bubbles before you read. A bubble means you drew less liquid than the mark says.
If your dose lands under about 5 units, reconstitute with more water so it lands somewhere readable. The dose does not change, only the volume it arrives in.

Work out your own number

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25 printable pages: dosing cards for the twelve most-used compounds at three water volumes, titration planners, a vial log, and five pages on what to do when it has already gone wrong.

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The maths is openThe formula is on every page and in the methodology. The code is one file with an automated test suite, run before each deploy.

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ReviewedDose ranges and half-lives checked 3 September 2026.

Why the units mix-up matters. Prescriptions and vial labels are in mg, syringes are in units. The ECRI patient-safety note on GLP-1 errors and the FDA statement on unapproved GLP-1 drugs both describe dosing errors; more reading is on our trusted resources page.

Common questions

How many units is 1 mL on an insulin syringe?: On a U-100 syringe, 1 mL is 100 units, so one unit is 0.01 mL. On a U-40 syringe, 1 mL is 40 units, so one unit is 0.025 mL. Almost every syringe sold for human use is U-100.
What is the difference between a 0.3 mL, 0.5 mL and 1 mL insulin syringe?: Only the total capacity. All three are U-100, so a unit means the same volume on each. A 0.3 mL barrel holds 30 units, a 0.5 mL holds 50, a 1 mL holds 100. The smaller barrel spreads those units over the same physical length, which makes small doses easier to read accurately.
How do I know if my syringe is U-100 or U-40?: It is printed on the barrel or the wrapper. U-40 syringes are usually veterinary and often have a red plunger. If you use a U-40 syringe with numbers worked out for U-100 you will draw two and a half times the intended dose.
What does 20 units mean in mL?: On a U-100 syringe, 20 units is 0.2 mL. The mass of peptide in that 0.2 mL depends entirely on how concentrated your vial is.

MethodologyEvery formula and rounding rule, so you can check the maths Read a syringeU-100 vs U-40, and the 2.5x error Build a full protocolThe stack builder at Peptide Bureau, about two minutes

Common conversions

The same three-step maths, pre-filled for the doses people ask about most. Units on a U-100 insulin syringe, where 100 units is 1 mL.

mg to units calculator Any dose at any concentration, both directions, with the full reference tables
Units to mg calculator What the units you drew are in milligrams
1 mg to units The most-asked conversion, at every common setup

Related calculators and charts

Tools

Peptide calculator The general tool, any compound
Reconstitution calculator How much water to add, and why it matters
Bacteriostatic water calculator Pick a volume that lands where you can read it
How to read an insulin syringe (this page)
The Protocol Pack Free 25-page printable reference
mg to units calculator Both directions, any concentration, with the reference tables
1 mg to units on an insulin syringe The conversion table for every common concentration
Units to mg calculator The mark you drew, back into milligrams
Methodology Every formula, assumption and rounding rule
About Peptulator Who publishes it, independence and contact
Embed the calculator Free widget for blogs, clinics and newsletters, credit link only

Every one of the 27 compound calculators, charts and tools: the full list.

Before you use these numbers This is a unit-conversion tool. It turns a vial strength and a water volume into a concentration, a draw volume and a syringe mark. It does not tell you what to take, whether to take it, or whether a compound is safe for you. Most compounds listed are sold for laboratory research and are not approved for human use. Nothing here is medical advice. Dosing decisions belong with a licensed clinician who knows your history. Always check the strength printed on your own vial rather than trusting a preset.