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Syringe unit converter
Convert between U-100 and U-40 insulin-syringe units, see the underlying volume in mL, and optionally translate units into milligrams using your vial's concentration.
Inputs
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Optional: estimate the dose in mg
Enter your vial size and how much bacteriostatic water you added.
Result
Live-computed.
Same volume on a U40 syringe
10 units
25 U100 units = 0.250 mL
- Volume
- 0.250 mL
- Estimated dose
- —
Add vial size and BAC water to also see the dose in mg.
Informational only — not medical advice. Verify with your clinician.
How syringe unit scales work
Insulin syringes are graduated in units, not milliliters. A unit is a fixed fraction of a milliliter that depends on the syringe scale: U-100 = 100 units per mL (1 unit = 0.01 mL) and U-40 = 40 units per mL (1 unit = 0.025 mL). The number printed at the same physical mark therefore means a different volume on each scale.
Converting between scales
The conversion is pure volume math: mL = units ÷ units-per-mL, then target units = mL × target units-per-mL. A 0.5 mL draw is 50 units on a U-100 syringe and 20 units on a U-40 syringe.
From units to milligrams
Units only become a dose once you know the vial's concentration (mg per vial ÷ mL of bacteriostatic water). Enter both optional fields above to see the mg estimate, or use our reconstitution calculator to work forward from a target dose instead.
FAQ
- What is the difference between U-100 and U-40 syringes?
- U-100 syringes hold 100 units per milliliter; U-40 syringes hold 40 units per milliliter. The same printed unit mark therefore represents a different liquid volume on each scale — 50 units is 0.5 mL on U-100 but 1.25 mL on U-40.
- How do I convert U-100 units to U-40 units?
- Divide the U-100 units by 100 to get milliliters, then multiply by 40. For example, 25 U-100 units = 0.25 mL = 10 U-40 units. This converter does the math instantly and can also estimate the dose in mg if you enter your vial size and bacteriostatic water volume.
- How many mg is one syringe unit?
- It depends entirely on the concentration of the reconstituted vial. One U-100 unit is 0.01 mL, so at 5 mg/mL one unit holds 0.05 mg. Enter your mg per vial and BAC water amount in the optional fields to see your exact mg per draw.
- Which syringe scale should I use?
- Use whatever scale is printed on the syringe in your hand — never assume. U-100 is standard in the US and most of Europe; U-40 appears in some regions and veterinary supplies. Mixing the two scales up is one of the most common measurement errors, which is exactly why this converter exists.
This page is for informational purposes only and is not medical advice. Always verify dosing with a licensed clinician.