Reconstitution calculator
Two numbers in, two numbers out, and one question it will not answer.
Enter what the vial says and how much diluent went into it. The calculator returns the concentration in mg/mL and how much compound sits in a single syringe unit at the calibration you choose. There is no field for an intended dose and no output telling you how many units to draw — that is a deliberate limit, not a missing feature.
What it computes
Concentration = vial amount / diluent volume. From there, one unit is a fixed fraction of a millilitre — 0.01 mL on a U-100 barrel — so the amount sitting in one unit is the concentration divided by the units per mL of that barrel.
Both outputs describe the vial in front of you. Neither depends on what you plan to do with it, which is exactly why they can be published without qualification. Illustrative numbers: a vial labelled 5 mg with 2 mL of diluent gives 2.5 mg/mL, and at U-100 one unit of that solution carries 0.025 mg — 25 mcg.
| In | Out |
|---|---|
| Vial amount and unit, as printed | Concentration, in amount per mL |
| Diluent volume actually added | Amount contained in one syringe unit |
| Syringe calibration (U-100, U-50, U-40) | Both figures restated in mcg where it helps |
What it deliberately does not do
There is no field for a target dose, and no output saying how many units to draw. That is the whole design decision, and it is worth being explicit about because most calculators ranking for these questions do precisely the opposite.
Software that takes a person's intended dose and returns an amount to administer is doing something other than arithmetic — under EU guidance it can fall within the definition of medical device software. Pinned's Terms state that it does not recommend compounds, sources, doses, or protocols, and a calculator answering "how much do I inject" would contradict them. The syringe units guide sets out the last step in full so you can carry it out yourself, with the decision staying where it belongs.
- No dose field, and no units-to-draw output.
- No suggested diluent volume — that is an input, from the product's labelling and whoever supplied the vial.
- No pre-filled example values, because a number sitting in a field is read as a recommendation.
- No compounds named, no sources, no vendor links.
- Incompatible units are refused rather than approximated — notably IU, which has no general conversion to mass.
How to read the output
Concentration describes the solution rather than the vial: it is how much compound each millilitre carries after reconstitution, and it moves with the diluent volume you entered, not with anything printed on the label.
Amount per unit takes that same solution and expresses it in the marks of the barrel you selected. It answers "what is in one mark", which is a fact about the vial and the syringe together. It does not answer "how many marks", because that requires an amount, and the amount is not something this page has any business holding.
Change the calibration and the per-unit figure changes while the concentration does not — the liquid is identical, the ruler is different. If that feels counterintuitive, the syringe units guide is the one to read next.
The app does one step more, and why that is different
The concentration arithmetic in Pinned is identical to this page. The app additionally converts an amount you enter into a draw volume and the units it corresponds to — because there you are recording a decision you have already made, against a vial that exists in your cabinet, rather than being handed an answer by a public page that knows nothing about you.
The boundary itself does not move. In the app as here, Pinned calculates from values you entered and reference identity data, and recommends no compounds, doses, stacks, sources, or protocols.
If the numbers look wrong
In practice the answer is in the inputs, and it is usually one of four things.
- Units: a vial in mg against an amount in mcg is a factor of 1000, and it looks plausible in both directions.
- Diluent volume: enter what actually went in, which is not always what was planned.
- Calibration: U-100, U-50 and U-40 give different per-unit figures for the same solution. Pick the barrel you are holding.
- IU: it does not convert to mass generically, so a refusal there is the correct answer rather than a bug.
Pinned converts numbers you enter. It does not recommend compounds, sources, doses, diluent volumes, or protocols, it is not a medical device, and nothing here is medical advice. Always verify calculations yourself against the product's own labelling.
FAQ
- What does the calculator need from me?
- Three things: the amount printed on the vial with its unit, the volume of diluent that went in, and which syringe calibration you are using. It asks for nothing about you and nothing about your intentions.
- Does it tell me how much bacteriostatic water to add?
- No. The diluent volume is something you enter, not something the calculator picks. That figure comes from the product's labelling and from whoever prescribed or supplied the vial; the calculator shows what any volume you enter works out to.
- Why does it not just tell me the units for my dose?
- Because that crosses from describing a vial into directing treatment, which is the line Pinned's Terms draw and which EU guidance treats seriously. The syringe units guide explains the conversion in full so you can carry it out, keeping the decision with you.
- Why does it refuse my units?
- Because the two units cannot be compared. Mass units convert cleanly, but IU measures biological activity and its conversion to milligrams is specific to each substance and preparation. Producing a number there would mean inventing one.
- Does it store what I type?
- No. The calculation runs entirely in your browser, nothing is sent anywhere, and the values never appear in the page address. If you want numbers kept against a real vial over time, that is what the app's cabinet is for.
- Is this the same maths the app uses?
- The concentration step is identical. The app additionally converts a dose you enter into a draw volume, because there you are recording your own decision rather than being handed one by a public page.
Last updated 2026-08-08 · Kurt Bijl