Vial math, done right. With the working shown.

Mixing math and U-100 syringe units for what your provider prescribed, plus a private dose log and reminders stored only on your device. We don't receive them.

Open the calculator My dose log

Example:0102030405060708090100U-100 · 100 units40 units = 0.40 mL

Why VialMath

Shows every step

See the exact arithmetic behind every number, so you can check it against your pharmacist's instructions.

Built-in math checks

Flags some common errors, like a dose larger than the whole vial or a draw that won't fit your syringe. Checks can't catch every mistake.

Private by design

No account, no ads, no third-party trackers. Only anonymous page counts. Your log is stored only in this browser.

Never suggests a dose

Every dose field starts empty. You enter what your prescriber wrote; we do the math.

Guides

How reconstitution math works

A plain-English walkthrough of reconstitution math: concentration = mg ÷ mL, volume = dose ÷ concentration, and units on a U-100 syringe.

Reading a U-100 syringe

U-100 means 100 units per mL. Learn how 30, 50, and 100-unit syringes are marked and how to convert units to mL.

Multi-dose vials: turning mg into syringe units

If your prescribed dose is in mg but your syringe is marked in units, here's the math using the concentration on your pharmacy label.

Tip: add VialMath to your home screen from your browser's share menu to use it like an app, even offline.

Not medical advice. This tool does arithmetic on numbers you enter. It does not recommend doses. Confirm with your prescriber or pharmacist. 18+ only.