Using a peptide reconstitution calculator, step by step

By Tessaro Pty Ltd · Reviewed November 2026 · For adults 18+

Reconstituting a vial means adding a measured volume of liquid to a powder so it can be injected. Once that is done, one piece of arithmetic remains, and the free peptide reconstitution calculator on this site does it: from the amount in the vial, the liquid you added and the amount you were prescribed per injection, it calculates the volume that holds that amount. This guide explains each field, where its number comes from, and how to check the answer. It never suggests a dose.

The three fields, and where each number comes from

• Vial amount — the amount of powder in the vial, printed on the vial or the pharmacy label. Enter it in the unit on that label. If the label is unclear, ask the pharmacist who dispensed it before you mix anything.
• Diluent (bacteriostatic water) added — the volume of liquid that actually went into the vial, in millilitres. Use the volume you were told to add and did add, not the size of the bottle it came from.
• Your dose — the amount per injection that your prescriber gave you. The field starts empty and has no default; the tool never fills it in or proposes a figure.

All three must describe the same vial, mixed the same way. A new vial, or the same vial size mixed with a different volume of liquid, needs all three entered again.

What the arithmetic does

There are two steps, and both are simple division. First, the strength after mixing: the vial amount divided by the volume of liquid added gives the amount in each millilitre. Second, the volume per injection: your prescribed amount divided by that strength gives the volume, in millilitres, that holds it.

The answer is also shown as the mark to fill to on a U-100 insulin syringe. A U-100 syringe is scaled so that a full millilitre reads 100 on its barrel, so the mark is the volume multiplied by a hundred. If your syringe is a different type, its markings will not match the answer, and you should ask your pharmacist how to read it.

Nothing else goes into the answer. The tool does not know what the medicine is, how it should be stored, or what anyone should take. It is a check on division, nothing more.

Check the answer before you rely on it

• Use the same unit for both — if the vial label is in milligrams and your prescribed amount is in micrograms, convert one so both use the same unit. There are a thousand micrograms in a milligram. A mismatch here puts the answer out by a factor of a thousand.
• Sense-check the size — the volume per injection can never be more than the liquid you added. If it is, one of the fields is wrong.
• Enter it twice — clear the fields and type everything again from the labels. Two matching answers rule out most typing slips.
• Compare with your instructions — if the answer differs from what your prescriber or pharmacist told you, follow their instructions and ask them about the difference. Do not split the difference.
• Write it down — the date you mixed the vial, the liquid and volume you added, and the use-by date from the label or your pharmacist.

What the tool does not do

It does not suggest an amount per injection, a schedule, or how much liquid to add. It does not check what is in the vial or whether it has been stored correctly. It is not a medical device, and it is not medical advice. Every number in it is one you typed, and the answer is only as good as those numbers.

For the reasoning behind the arithmetic in more detail, see the plain-English guide to reconstitution maths, and for what to note each time you mix a vial, see what to record when you reconstitute a vial.

Keeping the record afterwards

Once a vial is mixed, what matters over the following days is the record: the date it was mixed, what was added, and the date it should be used by. Memory is unreliable for this, especially with more than one vial in the fridge.

The Pepti app keeps that record with each vial. You enter the reconstitution date and your own use-by date, and it reminds you before each one.

Common questions

What do I need to use a peptide reconstitution calculator?

Three numbers: the vial amount from its label, the volume of liquid you added, and the amount per injection your prescriber gave you. The tool works out the volume that holds that amount and the matching mark on a U-100 insulin syringe.

Does the tool suggest how much to take?

No. The dose field starts empty and has no default, and the tool never suggests a dose, a schedule or a volume of liquid to add. Those come from your prescriber.

Why does the answer not match the marks on my syringe?

The answer is given for a U-100 insulin syringe. Other syringe types are marked differently, so the marks will not line up. Ask your pharmacist how to read the syringe you have.

Do I need to re-enter everything for a new vial?

Yes. The strength after mixing depends on both the vial amount and the volume of liquid added, so a new vial, or the same vial size mixed differently, needs all three fields entered again.

This guide explains arithmetic only. It does not recommend any substance, amount, volume or schedule; follow the instructions of your prescriber or pharmacist.

For adults 18+. Not medical advice. Pepti is a record-keeping tool, not a medical device.

Written with AI assistance and checked by Tessaro Pty Ltd. Not medical advice.

Pepti – Peptide Tracker · Guides · Reviewed November 2026 · Editorial policy · About