PeptulatorReconstitution and dosing maths

Peptide calculator

Vial, water and dose in. The reconstitution maths, the draw in mL and the exact mark on an insulin syringe out. Free, no signup, 27 compounds.

Peptulator, peptulator.com. Research use only, not medical advice.

The Protocol Pack, free

25 printable pages: dosing cards for the twelve most-used compounds at three water volumes, titration planners, a vial log, and five pages on what to do when it has already gone wrong.

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IndependentThis site does not sell peptides and is not owned by a vendor.
The maths is openThe formula is on every page and in the methodology. The code is one file with an automated test suite, run before each deploy.
How it earnsAffiliate links on one marked page, never inside the calculator.
ReviewedDose ranges and half-lives checked 3 September 2026.

How the maths works

Every reconstitution calculation is the same three steps, and once you have seen them you can check any calculator's answer by hand.

Step one, concentration. Divide the peptide in the vial by the water you added. A 10 mg vial with 2 mL of bacteriostatic water is 10 / 2 = 5 mg per mL.

Step two, volume. Divide your dose by that concentration. A 2 mg dose at 5 mg/mL is 2 / 5 = 0.4 mL.

Step three, units. A standard U-100 insulin syringe holds 100 units in 1 mL, so multiply the volume by 100. 0.4 mL is 40 units, which is the 40 mark on the barrel.

The one that catches people out is U-40 syringes, which are usually veterinary. They hold 40 units in 1 mL, so the same 0.4 mL is 16 units, not 40. Check which scale is printed on your barrel before you draw.

1 mL100 units20u01020304050607080901000.5 mL50 units20u051015202530354045500.3 mL30 units20u051015202530

The same 0.2 mL drawn on all three common insulin syringes. The volume is identical; only the number you read off the barrel changes.

How much bacteriostatic water should I add?

There is no single correct amount. The water does not change the dose, only how far along the barrel that dose lands. More water means a bigger, easier-to-read draw of a weaker solution. Less water means a small, concentrated draw that is harder to measure precisely.

The practical rule is to pick a volume that puts your usual dose somewhere between roughly 10 and 50 units, because that part of the barrel is easy to read and small errors matter least. If the calculator tells you to draw 3 units, add more water. If it tells you to draw 90 units, add less.

Whatever you choose, write it on the vial. A week later the number means nothing if you cannot remember how much water went in.

Common questions

How do I convert a peptide dose into insulin syringe units?
Divide the milligrams in the vial by the millilitres of bacteriostatic water to get the concentration in mg/mL. Divide your dose by that concentration to get the volume in mL. Multiply by 100 for units on a standard U-100 insulin syringe. For example, 10 mg in 2 mL is 5 mg/mL; a 2 mg dose is 0.4 mL, which is 40 units.
Does adding more bacteriostatic water change my dose?
No. The amount of peptide in the vial is fixed. Water only changes the concentration, so it changes how many units you draw for the same dose. More water means a larger, easier to read draw of a weaker solution.
How many units is 1 mL on an insulin syringe?
On a standard U-100 insulin syringe, 1 mL is 100 units. On a U-40 syringe, usually veterinary, 1 mL is 40 units. Check the scale printed on your barrel before drawing.
What is the difference between mg and mcg?
1 mg equals 1000 mcg. GLP-1 compounds such as retatrutide, tirzepatide and semaglutide are usually dosed in mg. Repair and growth-hormone peptides such as BPC-157, ipamorelin and sermorelin are usually dosed in mcg.
How many doses are in a vial, and how long will it last?
Divide the amount in the vial by your dose and round down. A 10 mg vial at 2 mg per dose is 5 doses; once weekly, that is 35 days. The calculator shows both as Doses per vial and Vial lasts.
Is this calculator medical advice?
No. It is a unit-conversion tool. It converts a vial strength and a water volume into a draw volume and a syringe mark. It does not decide what you should take. Most compounds listed are sold for research use only and are not approved for human use.

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Tools

Before you use these numbers This is a unit-conversion tool. It turns a vial strength and a water volume into a concentration, a draw volume and a syringe mark. It does not tell you what to take, whether to take it, or whether a compound is safe for you. Most compounds listed are sold for laboratory research and are not approved for human use. Nothing here is medical advice. Dosing decisions belong with a licensed clinician who knows your history. Always check the strength printed on your own vial rather than trusting a preset.