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Peptide dose calculator
Enter your vial size, how much bacteriostatic water you mixed in, and your target dose. See exactly where to draw to on a U-100 or U-40 insulin syringe — including when a dose needs to be split across multiple draws or is too small to measure.
Verify with your prescriber or pharmacist before drawing any dose.
This is an educational calculator, not medical advice. It performs arithmetic on the numbers you enter and does not know your prescription or what is appropriate for you.
How the calculation works
Working out how many units to draw is a two-step conversion. First you find the concentration of the reconstituted vial: the milligrams of peptide in the vial divided by the milliliters of bacteriostatic water you added. A 10 mg vial mixed with 2 mL of water gives a concentration of 5 mg/mL.
Second, you convert your dose into a volume and then into syringe units. Divide the dose (in milligrams) by the concentration to get the volume in milliliters, then multiply by the units-per-mL printed on your syringe. On a U-100 syringe there are 100 units in every milliliter, so 0.1 mL reads as 10 units. On a U-40 syringe the same 0.1 mL reads as 4 units, which is why the scale of the syringe in your hand matters.
Why the syringe scale matters
The “U” number describes the barrel markings, not the medication. A U-100 and a U-40 syringe hold the same physical volume, but they number it differently. If you read the units off the wrong scale you will draw the wrong amount, so this tool asks you to pick the exact syringe type and size you are using and marks the fill point accordingly.
When a dose is hard to measure
Very small doses can fall below one unit on the syringe, where measurement error becomes large. When that happens, reconstituting the vial with more bacteriostatic water lowers the concentration so the same dose occupies more units and becomes easier to read. The reverse is also true: too little water produces a concentration so high that small differences in the plunger position translate into large differences in dose. There is no universally correct amount of water — it is a tradeoff between injection volume and measurement precision, and the right choice depends on your prescription. Decide it with your prescriber or pharmacist.
What this tool does not do
This calculator does not recommend a dose, a schedule, or a peptide. It does not know your prescription or your health history. It only takes the numbers you provide and shows the arithmetic on a syringe so the result is easier to picture. Every dose and draw amount should be confirmed with a licensed professional before you act on it.
Related tools: reconstitution concentration reference and syringe unit converter.
FAQ
- How do I calculate syringe units for a peptide dose?
- First find the concentration by dividing the mg in the vial by the mL of bacteriostatic water you added. Divide your dose (in mg) by that concentration to get the injection volume in mL, then multiply by the units-per-mL of your syringe (100 for a U-100 syringe, 40 for a U-40). This tool does that math visually and marks the result on a syringe. Always confirm the actual amount with your prescriber or pharmacist.
- What is a U-100 syringe?
- A U-100 insulin syringe is graduated so that 100 units equals 1 mL — each unit is 0.01 mL. It is the most common insulin syringe. U-100 refers to the barrel markings, not the medication; the same syringe can measure a volume of any solution.
- How much bacteriostatic water should I add?
- There is no single correct amount — it is a tradeoff. Adding more water lowers the concentration, which makes small doses easier to measure but increases the injection volume. Adding less water raises the concentration and shrinks the volume, but tiny doses become harder to draw accurately. The right amount depends on your prescribed dose and vial size, so decide it with your prescriber or pharmacist rather than following a generic number.
- What if my dose is less than 1 unit on the syringe?
- A dose under 1 unit is very difficult to measure accurately on a standard insulin syringe. Reconstituting the vial with more bacteriostatic water lowers the concentration so the same dose occupies more units and becomes measurable. The calculator flags this case and suggests a BAC water volume that would move the dose into a readable range — but confirm any change with your prescriber or pharmacist.
- What is the difference between U-40 and U-100 syringes?
- The number is the units-per-mL on the barrel. A U-100 syringe has 100 units per mL; a U-40 syringe has 40 units per mL. That means the same volume reads as a different number of units on each: 0.25 mL is 25 units on a U-100 but 10 units on a U-40. Using the wrong scale for your syringe changes the number you draw, so always match the calculator to the syringe in your hand.
- Is this medical advice?
- No. This is an educational tool that performs arithmetic on the numbers you enter. It does not know your prescription, your health, or what dose is appropriate for you, and it is not a substitute for professional guidance. Verify every dose and draw amount with a licensed prescriber or pharmacist.
This page is for informational purposes only and is not medical advice. Always verify dosing with a licensed clinician.