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Reconstitution Calculator

Avoid reconstitution mistakes: enter your vial amount, the water you added, and your dose to get the exact mark to draw to on an insulin syringe. Free, no sign-up.

Shows every step of the math · Updated July 2026

mg
mL
mg

Draw to 40 units, 0.4 millilitres.

Draw to40units
Volume0.4mL
Syringe size
Same units either way. A smaller barrel just spreads them out.
10 mgumL00200.2400.4600.6800.81001.0
Concentration5 mg/mL
Each unit is50 mcg
Doses per vial5
Runs out in5 days
Discard byMon, Aug 24, 2026 · 28 days if mixed today
Frequency
How much water?

More water dilutes it, so the same dose takes more units: easier to read, fewer per vial. Where each lands:

1 mL20 ulands clean
2 mL40 ulands clean
3 mL60 ulands clean
Printable card
concentration = 10 mg ÷ 2 mL = 5 mg/mL
units = (2 mg ÷ 5 mg/mL) × 100 = 40 u
doses = 10 mg ÷ 2 mg = 5

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What the marks on a U-100 syringe mean

U-100 describes the scale: the barrel is graduated 100 units to the millilitre, so one unit is 0.01 mL. Drag the slider to see where any reading sits on the barrel and what it is in mL.

0.4mL
020406080100
Units are a volume, not a dose. The mark you draw to is just how far up the barrel the liquid goes: 40 units is 0.4 mL. How much compound that contains depends on the concentration, which is why the same dose lands on a different mark when you change the water.

The conversion

  • 100 units = 1 mL
  • 50 units = 0.5 mL
  • 10 units = 0.1 mL
  • 1 unit = 0.01 mL

Barrel sizes

U-100 syringes come in 0.3 mL (30-unit), 0.5 mL (50-unit), and 1 mL (100-unit) barrels. They all use the same U-100 scale; a smaller barrel just holds fewer total units with wider spacing between them, which makes a small draw easier to read accurately.

Check the barrel says U-100. U-40 syringes exist, mostly for veterinary insulin, and use a different scale of 40 units per mL. Reading a U-100 figure on a U-40 barrel misreads the volume. This calculator assumes U-100.

Save a vial and it counts down

For each vial you save, it keeps the strength, the units to draw, and how many doses are left, and counts down the days until you should throw it out. Add the discard date to your own calendar in one tap, so you get a reminder without an app or an account. Everything stays in your browser and nothing is sent anywhere.

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Common questions

How do I calculate reconstitution?
Concentration = vial amount (mg) ÷ water added (mL). To find the volume for a dose, divide the dose by that concentration. On a U-100 insulin syringe, 1 mL = 100 units, so multiply the volume in mL by 100 to get units. This calculator does all three steps for you.
How many units is a dose on an insulin syringe?
It depends on the concentration. Example: a 5 mg vial with 2 mL of water is 2.5 mg/mL. A 250 mcg (0.25 mg) dose is 0.1 mL, which is 10 units on a U-100 syringe. Change the water volume and the units change, which is why the calculator recomputes live.
What does “units to draw” mean?
It is the mark on a standard U-100 insulin syringe you pull the plunger back to. A U-100 syringe is graduated 0 to 100 units over 1 mL, so the units reading is simply the draw volume in mL times 100.
Does more water change the dose?
No. The amount of active compound per dose is set by your dose figure, not the water. More water only makes the solution more dilute, so you draw more units for the same dose. Water is about landing on a clean, easy-to-read mark, not about strength.
How many units are in 1 mL?
100 units on a U-100 insulin syringe. That is what “U-100” means: the barrel is graduated 100 units to the millilitre, so each single unit is 0.01 mL.
How many units is 0.5 mL on a U-100 syringe?
50 units. On the U-100 scale, 100 units equals 1 mL, so half a mL is 50 units. The scale under the syringe in the calculator shows this conversion at every mark.
What is the difference between U-40 and U-100 syringes?
The scale. U-100 is 100 units per mL; U-40 is 40 units per mL. They are not interchangeable; mixing them up misreads the volume. Confirm your syringe says U-100 before drawing, since this calculator assumes the U-100 scale.
Is this calculator free?
Yes. Free, no sign-up, and no account needed to use it. You can optionally get occasional measurement guides by email, but the calculator itself is fully open.