Peptide reconstitution calculator
Enter what’s in the vial, how much water you added and your prescribed dose. See how many units to draw on an insulin syringe, and the math behind the number.
Math checked on September 15, 2026, with 13 automated tests. Free, no sign-up, and pep.red sells nothing.
Not a recommendation to use anything. This calculator does the math for a dose a healthcare professional already prescribed. It never suggests a dose, a peptide or a protocol.
What’s in the vial
The number on the label, in milligrams.
How much water you added
Water doesn’t change the dose. It only changes where the dose lands on the syringe.
Which syringe
It’s printed on the barrel or the box.
How far apart the marks areLook at the small lines between two numbers. It varies by manufacturer.
Your prescribed dose
This page never suggests a dose. Enter the one you were prescribed.
250 mcg equals 0.25 mg. Mixing them up changes the dose a thousandfold.
Draw the plunger to
10 units
That’s 0.10 mL of liquid holding 250 mcg.
0.5 mL syringe, U-100 scale, marked every 1 unit.
- Concentration
- 2.5mg per mL
- Per dose
- 0.10mL
- In the vial
- 20doses, by the math
- Fits in the syringe.Uses 20% of the 0.5 mL syringe.
- Lands right on a mark.This syringe is marked every unit, and 10 is one of the marks.
The math, with your numbers
Three steps. If any of them doesn’t match what’s in your hands, stop here.
- Concentration: vial divided by water
- 5 mg ÷ 2 mL = 2.5 mg/mL
- Volume: dose divided by concentration
- 0.25 mg ÷ 2.5 mg/mL = 0.10 mL
- Mark: volume times the syringe scale
- 0.10 mL × 100 units per mL = 10 units
What the syringe number measures
The most common insulin syringe is U-100: every milliliter has 100 marks, called units 2. Ten units are 0.10 mL.
The mark measures volume, not peptide. How much peptide sits in ten units depends on how much powder was in the vial and how much water went in. That is the math this calculator does.
Mark spacing changes between syringes. 0.3 mL syringes are marked every unit or every half unit; 0.5 mL every unit; 1 mL usually every 2 units 3. Some 1 mL models are marked every unit 2. That’s why the calculator asks about yours.
The five most common math errors
- Mixing up mcg and mg. A milligram is a thousand micrograms. The mix-up changes the dose a thousandfold. The abbreviation "µg" is mistaken for "mg" often enough to make ISMP’s list of error-prone abbreviations, which recommends writing "mcg" 1.
- Dropping the leading zero. "0.5" written as ".5" has been read as 5 1. This calculator always shows the zero.
- Reading a comma as a decimal point. In English, "1,500" is one thousand five hundred. In Portuguese, it’s one and a half. The calculator accepts both and warns when a number could be read either way.
- Using a U-40 syringe as if it were U-100. On a U-40, 1 mL is 40 units. The same volume shows a different number. The FDA-approved label of a veterinary insulin warns that using another syringe results in incorrect dosing 4.
- Rounding to a mark that doesn’t exist. If the math gives 2.5 units on a syringe marked every 2 units, there is no mark 3. The calculator shows how far off each neighboring mark is.
Table: units and milliliters
| Syringe units | mL on U-100 | mL on U-40 |
|---|---|---|
| 1 | 0.010 | 0.025 |
| 2 | 0.020 | 0.050 |
| 4 | 0.040 | 0.100 |
| 5 | 0.050 | 0.125 |
| 10 | 0.100 | 0.250 |
| 15 | 0.150 | 0.375 |
| 20 | 0.200 | 0.500 |
| 25 | 0.250 | 0.625 |
| 30 | 0.300 | 0.750 |
| 40 | 0.400 | 1.000 |
| 50 | 0.500 | 1.250 |
| 60 | 0.600 | 1.500 |
| 70 | 0.700 | 1.750 |
| 80 | 0.800 | 2.000 |
| 90 | 0.900 | 2.250 |
| 100 | 1.000 | 2.500 |
What no calculator knows
- Whether the vial holds what the label says. The calculator trusts the printed number. If the real content differs, every mark carries a different dose, and nothing on this screen can tell.
- Whether the dose is right for you. pep.red doesn’t prescribe, recommend protocols or say anything is safe for you.
- How much gets lost. A little liquid stays in the vial and in the syringe hub. The dose count is the ceiling of the math.
- How to mix, store and inject. Sterility, shelf life after mixing and injection technique are outside this calculation.
Frequently asked questions
How many units are in 1 mL on an insulin syringe?
On a U-100 syringe, the most common kind, 1 mL is 100 units. So 10 units are 0.10 mL and 25 units are 0.25 mL 2.
Does the syringe unit measure how much peptide is inside?
No. The mark measures volume. How much peptide each mark holds depends on how much powder was in the vial and how much water was added. The calculator does that math.
What’s the difference between U-100 and U-40 syringes?
Does the amount of water change the dose?
It doesn’t change how much peptide is in the vial. It changes the concentration, and with it the mark where the same dose lands. More water, more units for the same dose.
How do I convert mcg to mg?
Divide by a thousand: 250 mcg is 0.25 mg. ISMP recommends writing "mcg" rather than "µg", because "µg" gets mistaken for "mg" 1.
Why does the result fall between two marks?
Because syringes are only marked every 1 or 2 units, depending on the model 3. The calculator shows how far off each neighboring mark is. Whoever prescribed the dose decides what to do with that.
Sources
- 1Institute for Safe Medication Practices. ISMP List of Error-Prone Abbreviations, Symbols, and Dose Designations. 2024. Accessed 15/09/2026.
- 2MedlinePlus, National Library of Medicine (EUA). Giving an insulin injection. 2024. Accessed 15/09/2026.
- 3Ghoshal M; revisão médica de Biggers A. Healthline. Insulin Syringe Sizes and Lengths: Importance and How to Choose. 2025. Accessed 15/09/2026.
- 4DailyMed, National Library of Medicine (EUA). Vetsulin (porcine insulin zinc suspension), bula aprovada pela FDA. 2026. Accessed 15/09/2026.