The Peptide Calculator

Diluent volume for a target concentration

Enter the vial strength and the concentration you want. This solves for the volume rather than the strength.

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

Fill in the fields above to see the answer.

Read this with the answer

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.

Most compounds named here are 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. Full disclaimer.

Show the working
  1. Rearranging c = m / V gives V = m / c. A 10 mg vial at a target of 2 mg/mL needs 5 mL of finished solution.
  2. That answer is the FINISHED volume, not the diluent to add. The diluent is the finished volume minus the space the solid occupies, which is smaller by an unmeasured amount unless the displacement is known.
  3. Adding the full figure as diluent therefore lands slightly below the target concentration. For milligram quantities the gap is usually small against the error of drawing from a 1 mL barrel, but "usually small" is not zero and the page does not round it to zero on a reader’s behalf.

Why the answer is a solution volume and not an amount of diluent

The identity solves for the volume of liquid the compound ends up dissolved in. A reader adding that much diluent ends up with slightly more liquid than that, because the solid contributes its own volume, and so with a slightly weaker solution than the target.

There are two honest ways round it. Measure the finished volume after mixing and use the main calculator with that figure, which removes the uncertainty entirely. Or accept that the concentration is a little below the target and know which direction the error runs in. What is not honest is quietly treating the two volumes as the same number, which is the standard behaviour of calculators in this category.

Choosing a target concentration so the volume is measurable

A concentration is only useful if the volumes it produces can be read off the barrel in hand. At 10 mg/mL, a 100 mcg amount is 0.01 mL, which is one unit on a U-100 syringe and sits in the range where the reading error is a large share of the amount measured. The same amount in a more dilute preparation is a longer, more readable draw.

The arithmetic for that trade-off is on graduations and readability, which works through what a barrel marked every unit can and cannot show.

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