Two compounds, one vial

Two solids, one volume of liquid. Each has its own strength in that solution, and no draw can take one without the other.

Educational arithmetic only. Not medical advice and not a dosing protocol.

First one, as you label it

Its mass in the vial

Second one, as you label it

Its mass in the vial

Mass unit for both

Diluent put in Unit for diluent put in

Amount of the first you want Unit for amount of the first you want Fixing one fixes the other, and both are reported.

Which barrel Required. The printed numbers mean a different volume on each of these.

Fill the fields in and the answer appears here.

This tool does its arithmetic in the browser, so it needs JavaScript switched on. Each component can be worked separately with the vial strength tool, at the same diluent volume.

What the bench will not tell you

This is educational arithmetic on figures entered by the reader. It is not medical advice, not a dosing protocol, and not a recommendation that anything be prepared, obtained or administered.

Nothing here states what quantity is appropriate for anyone, and there is no function in it that produces an amount to administer. A question about anyone’s health belongs with a licensed clinician who can examine the person asking.

Compounds of the kind this arithmetic is used on are largely research chemicals that are not approved by the FDA for human use. An exact calculation is not an accurate measurement: what is actually in a syringe depends on the preparation and the device, neither of which this page can see.

No qualified clinical reviewer is recorded against this site, and no credential is claimed anywhere on it. the limits of this bench.

The arithmetic, step by step

Each component is concentrated against the WHOLE volume, not against a share of it: 10 mg of each in 2 mL is 5 mg/mL of each, not 5 mg/mL of the pair.
The solid that displaces volume is the total of both, so the ceiling on the strength bites harder here than for a single compound.
Because the volume is shared, the ratio in any draw is fixed by the masses that went in. Solving a volume from a target amount of one component determines the amount of the other in the same volume, and that figure is printed with it.

The mistake this tool exists to prevent

A vial with two compounds in it is not two vials. There is one solution and one volume, so any draw carries both components, in the proportion set when the vial was filled. Nobody drawing from it gets to pick one component's amount on its own.

A tool that lets a reader solve for one component and then shows only that component has concealed half of what is in the syringe. So this one always reports both: give a target for the first and the answer states the volume, the amount of the first in it, and the amount of the second that necessarily comes along.

The ratio belongs to the vial, not to the draw

A vial filled with 10 mg of one and 20 mg of the other is a 1:2 mix at every volume drawn from it, and no arithmetic downstream changes that. Changing the ratio means filling a different vial, not drawing differently from this one.

Which means a shared vial removes a degree of freedom. Two separate vials can be drawn independently; one shared vial cannot. That is a fact about the preparation, and it is why the ratio is printed next to the strengths.

Next to this on the bench

Strength of a mixed vial
The single-compound case.
Thinning a solution
For reducing a shared vial after the fact.
Displacement and the ceiling
Why two solids make the ceiling matter more.