Peptide reconstitution calculator

Most research peptides ship as a freeze-dried — also called lyophilized — powder sealed inside a small glass vial. The powder itself cannot be drawn into a syringe and cannot be measured by volume. Before any of that is possible, the powder has to be rehydrated by adding a precise amount of liquid. That step is reconstitution, and it is the foundation of every other calculation that follows.

The liquid added during reconstitution is almost always bacteriostatic water, often shortened to BAC water. It is sterile water that contains a very small amount of benzyl alcohol — usually 0.9 percent. The benzyl alcohol limits microbial growth inside a multi-use vial after the rubber stopper has been pierced for the first time, which is what makes BAC water different from plain sterile water for injection.

Once the powder dissolves into the BAC water, the contents of the vial become a solution with a measurable concentration. That concentration is what links the original mass on the vial label to the volume your syringe will eventually pull. Without a known concentration, every other number on a peptide page is just a guess.

Every reconstitution calculator on the internet — including this one — runs the same two-line equation. The first line solves for concentration. The second line solves for the volume you need to draw to hit a specific dose. The third number, units on a U-100 insulin syringe, is just that volume rescaled.

Concentration in milligrams per millilitre equals the milligrams of peptide originally in the vial divided by the millilitres of bacteriostatic water that you added. If you put 5 mg of peptide into 2 mL of BAC water, the concentration is 2.5 mg per mL. That single number now determines how every dose will be measured for the entire life of the vial.

Volume to draw in millilitres equals your desired dose in milligrams divided by that concentration. If your dose is 0.25 mg and the concentration is 2.5 mg per mL, you draw 0.1 mL. On a U-100 insulin syringe, 1 mL is 100 units, so 0.1 mL is 10 units. The calculator shows all three numbers — concentration, volume, units — at the same time so you do not have to convert manually.

There is also a fourth output: doses per vial. That is just the total milligrams in the vial divided by the milligrams in a single dose, rounded down to a whole number because a partial final dose at the bottom of a vial is rarely usable. Tracking doses per vial is what lets a logging app warn you when a vial is running low and a refill needs to be ordered.

A vial label only ever tells you how much peptide is inside. It almost never tells you how much BAC water to add — because that part is up to you. Two people can take the same 5 mg vial and reconstitute it with completely different volumes of water, ending up with completely different concentrations, and both can be entirely consistent with how peptides are typically prepared.

Adding more BAC water makes each draw a larger volume in millilitres, which translates to more units on an insulin syringe. That can be useful when typical doses are very small — drawing 4 units is much easier to read accurately on a syringe than drawing 0.4 units, especially when the syringe markings are densely spaced. People often add more diluent on purpose for low-dose peptides for exactly this reason.

Adding less BAC water concentrates the solution. The same dose now occupies a smaller volume, which means fewer units on the syringe and more total doses per vial before refilling. The tradeoff is precision: at very small unit counts, a one-unit error becomes a much larger percentage error in the actual dose delivered. Picking a sensible diluent volume is a real decision that the calculator helps you simulate quickly without committing to a vial.

Almost every peptide draw is measured on an insulin syringe rather than a tuberculin syringe, because the unit markings make small volumes much easier to read. A standard U-100 insulin syringe is calibrated so that 100 units of fluid fills exactly 1 millilitre. That single relationship — 100 units equals 1 mL — is the only conversion you ever need to memorize.

From there, the math is just multiplication. A 0.5 mL draw is 50 units. A 0.1 mL draw is 10 units. A 0.05 mL draw is 5 units. The reconstitution calculator outputs both volume and units side by side so you can pick whichever number is easier to read on the syringe in your hand.

U-40 insulin syringes also exist, mostly in veterinary contexts, and use a different calibration: 40 units equals 1 mL. Mixing up a U-40 and a U-100 syringe will lead to a dose that is off by a factor of 2.5. The calculator on this page assumes U-100, which is what nearly every peptide user is actually using.

The calculator solves the math. It does not pick a dose for you, it does not pick a frequency, it does not adjust for body weight or sensitivity, and it does not know anything about your specific situation. Those decisions belong to you and a licensed healthcare professional who can look at your bloodwork, your history, and your goals together.

It also does not validate the peptide itself. The calculator assumes the vial actually contains the milligrams printed on the label and that the peptide is properly reconstituted into a clear, fully dissolved solution. If a vial arrives clumped, cloudy, or visibly off, no amount of math fixes that. Reconstitution math only works on a vial that is in good condition to begin with.

Finally, the calculator does not log anything. Every input you type lives only on this page until you reload. The reason Peptide Pilot exists is to stop you from running these numbers from scratch every single dose: enter a vial once, and every subsequent draw, dose, and refill reminder is calculated and logged automatically.