Reconstitution math is simple. Getting it wrong is also simple. A vial is labelled in milligrams, the target amount is often written in micrograms, the water is measured in millilitres, and the syringe is marked in units. That's four different units in one small calculation, and a slip between any two of them is off by a factor of ten or a thousand.
We built the VialVerify calculator to do that conversion for you, show the answer as the one number you actually need, and flag the situations where the answer can't be right. This article walks through what it does and how to read it.
What you put in
Every result comes from three numbers:
- Vial powder (mg): how much powder is in the vial, as printed on the label.
- Water added (ml): how much bacteriostatic water goes into the vial.
- Target dose (mcg): how much you want in the syringe. 1 mg is 1,000 mcg.
You also choose the syringe size: 1.0 ml (100 units) or 0.5 ml (50 units). Both are U-100 syringes, so a unit means the same volume on either one. The choice only changes how much fits.
What it works out
The calculator does three steps, in this order:
A worked example
Take a 10 mg vial with 2.0 ml of water, and a target of 500 mcg:
| Step | Calculation | Result |
|---|---|---|
| Concentration | 10 mg ÷ 2.0 ml | 5 mg/ml (5,000 mcg/ml) |
| Volume | 500 mcg ÷ 5,000 mcg/ml | 0.100 ml |
| Units | 0.100 ml × 100 | 10 units |
Two ways to use it
Quick Presets
Pick a compound category, a vial and a dose from the dropdowns. Each vial comes with a set amount of water, which appears in the Mixing Recipe box, and each dose option has a set amount. There are no numbers to type, which removes the most common source of mistakes.
Custom Calculator
Three sliders let you set your own values:
- vial powder from 2 to 60 mg, in 1 mg steps;
- water from 0.5 to 5.0 ml, in 0.5 ml steps;
- target dose from 50 to 5,000 mcg, in 50 mcg steps.
The result updates as you drag, so you can see straight away how adding more or less water changes the draw.
Reading the result
The large number is the one that matters: the mark to draw to on the syringe, in units, rounded to the nearest 0.1. Everything else supports it:
- The volume in ml, next to the units, for anyone measuring by volume.
- The line underneath restates the dose and concentration, so you can check the calculator is working from the numbers you meant.
- The syringe graphic fills to the same mark on a scale that matches your syringe: 0 to 100 for 1.0 ml, 0 to 50 for 0.5 ml.
- Concentration and Mixing Recipe sit below. These depend only on the vial and the water, so they stay the same when you change the dose.
Built-in warnings
When an answer can't be drawn as calculated, the result turns amber, the status badge changes from ACCURATE MEASUREMENT to CHECK INPUTS, and a warning appears directly under the number. There are three:
- More than the vial holds. The dose is larger than the whole vial. A 5 mg vial can't provide 7,500 mcg.
- Too big for the syringe. The draw doesn't fit the selected syringe. 75 units won't fit in a 50-unit syringe; the graphic shows the overflow as well.
- Too small to measure. Under 2 units is below what the tick marks on a standard syringe can show reliably. Using less water raises the concentration, which makes the same dose a larger, measurable draw.
Languages and number formats
The calculator is available in English, and in Spanish and Portuguese on the Mexico and Brazil pages. Everything is translated, including the dropdown options and the warnings, and numbers follow local formatting: 0.250 ml in English and Spanish, 0,250 ml in Portuguese. Switching language keeps your selections.
Before you draw
The calculator does arithmetic. It doesn't decide what dose is right for anyone. The preset doses are examples of common values, not a recommendation. Confirm the dose with your prescriber or pharmacist.
A few quick checks catch most errors:
- Milligrams or micrograms? Make sure the dose is entered in mcg. 0.5 mg is 500 mcg, not 5.
- Is it a U-100 syringe? The results assume U-100, which is standard for insulin syringes in most countries. U-40 syringes are marked differently, and these unit numbers don't apply to them.
- Does the water match? The result is only right for the exact volume of water you added. If you added a different amount, change the water setting first.
- Read the line under the number. If the dose or concentration it shows isn't what you expected, one of the inputs is off.
You can open the calculator any time at vialverify.org/calculator.