Peptide Calculator for reconstitution, dose and syringe units
Enter the peptide in your vial, the bacteriostatic water you add and your dose. PeptideConvert shows the concentration, the exact volume and where to draw on a U-100 insulin syringe, with every step of the math and checks for the most common dosing errors.
- Error checks on every result
- U-100 and U-40 syringes
- Runs in your browser
Show the math
Quick answer
How does a peptide calculator work?
It turns three numbers into a syringe reading. Concentration = peptide (mcg) ÷ water (mL). Volume = dose (mcg) ÷ concentration. Units = volume (mL) × 100 on a U-100 syringe. For example, 5 mg in 2 mL gives 2,500 mcg/mL, so a 250 mcg dose is 0.1 mL, which is 10 units.
Every peptide calculation in one place
From mixing a vial to reading a lab sequence, each tool shows its formula, flags common mistakes and links to the next step.
Reconstitution & dosing
Mixing a vial, reading the syringe and planning doses.
GLP-1 peptides
Semaglutide, tirzepatide and retatrutide vial math.
Peptide-specific
Presets and reference data for individual peptides.
Converters
Units, mass and syringe conversions.
How to calculate a peptide dose in syringe units
Every dosing tool on this site uses the same three steps. Once you know them, you can check any result by hand.
- 1
Find the concentration
Divide the peptide in the vial (mg × 1000 = mcg) by the water you added in mL. 5 mg in 2 mL = 2,500 mcg/mL.
- 2
Work out the volume
Divide your dose in mcg by the concentration. 250 mcg ÷ 2,500 mcg/mL = 0.1 mL.
- 3
Convert to syringe units
Multiply the volume by 100 for a U-100 syringe. 0.1 mL × 100 = 10 units.
Peptide reconstitution chart: units for common doses
Units on a U-100 syringe for the most common vial and water combinations. Cells above 100 units need more than one full 1 mL syringe.
| Vial | Water | Concentration | mcg per unit | 100 mcg | 250 mcg | 500 mcg | 1 mg |
|---|---|---|---|---|---|---|---|
| 2 mg | 1 mL | 2 mg/mL | 20 | 5 u | 12.5 u | 25 u | 50 u |
| 2 mg | 2 mL | 1 mg/mL | 10 | 10 u | 25 u | 50 u | 100 u |
| 5 mg | 1 mL | 5 mg/mL | 50 | 2 u | 5 u | 10 u | 20 u |
| 5 mg | 2 mL | 2.5 mg/mL | 25 | 4 u | 10 u | 20 u | 40 u |
| 5 mg | 2.5 mL | 2 mg/mL | 20 | 5 u | 12.5 u | 25 u | 50 u |
| 10 mg | 1 mL | 10 mg/mL | 100 | 1 u | 2.5 u | 5 u | 10 u |
| 10 mg | 2 mL | 5 mg/mL | 50 | 2 u | 5 u | 10 u | 20 u |
| 10 mg | 3 mL | 3.33 mg/mL | 33.3 | 3 u | 7.5 u | 15 u | 30 u |
| 15 mg | 3 mL | 5 mg/mL | 50 | 2 u | 5 u | 10 u | 20 u |
| 20 mg | 2 mL | 10 mg/mL | 100 | 1 u | 2.5 u | 5 u | 10 u |
u = units on a U-100 insulin syringe (100 units = 1 mL). Computed with the same formulas as the calculator above.
Reading an insulin syringe: 0.3 mL, 0.5 mL and 1 mL
All three U-100 sizes use the same scale: 1 unit = 0.01 mL. Smaller barrels spread the same units over more length, so small doses are easier to read.
| Syringe | Holds | 1 unit = | Smallest mark | Best for |
|---|---|---|---|---|
| U-100 · 0.3 mL (30 units) | 30 units | 0.01 mL | 0.5 units | Small doses; finest markings (often half-unit) |
| U-100 · 0.5 mL (50 units) | 50 units | 0.01 mL | 1 unit | Everyday peptide doses up to 50 units |
| U-100 · 1 mL (100 units) | 100 units | 0.01 mL | 2 units | Larger volumes; marks usually every 2 units |
| U-40 · 1 mL (40 units) | 40 units | 0.025 mL | 1 unit | Veterinary insulin; not for “units” written for U-100 |
Graduations vary by brand. Check the markings printed on your own syringe.
Calculators with presets for specific peptides
These pages add common vial sizes, labelled or trial dose steps where they exist, storage data and regulatory status.
Built-in checks for the errors that cause overdoses
In 2024 the FDA reported patients taking 5 to 20 times their intended dose of compounded semaglutide, often because units, millilitres and milligrams were mixed up or the syringe was far larger than the dose. Every PeptideConvert calculator runs these checks on each result.
Calculations happen in your browser. Nothing you type is sent to a server.
- mg vs mcg mix-ups
Flags doses like “250 mg” that are almost always meant as 250 mcg.
- Dose larger than the vial
Stops you when a single dose needs more liquid than the vial holds.
- Dose too big for the syringe
Warns when the draw exceeds 30, 50 or 100 units and tells you what to change.
- Between syringe marks
Shows the nearest printed mark and the exact dose that mark delivers.
- Tiny, hard-to-read volumes
Flags draws under 2 units and explains how more water makes them readable.
- U-40 vs U-100 syringes
Explains the 2.5× error when units written for U-100 are drawn in a U-40 syringe.
What to know before you mix a peptide vial
Bacteriostatic vs sterile water
Bacteriostatic water contains 0.9% benzyl alcohol, which lets a vial be used for multiple draws. Sterile water has no preservative and is meant for single use. Use the diluent your product instructions specify.
Storage after mixing
Reconstituted peptides are usually kept refrigerated at 2–8 °C and protected from light. Follow the product label. For compounded multi-dose vials without other data, USP <797> defaults to 28 days after first puncture.
Water changes units, not dose
Adding more water spreads the same peptide through more liquid. The dose stays the same, but the number of units you draw goes up. Always recalculate if you change the water volume.
Peptide calculator questions, answered
Short, direct answers. Each one links to the tool that goes deeper.
How do I calculate how many units of peptide to inject?
Divide the peptide in the vial (in mcg) by the water you added (in mL) to get the concentration. Divide your dose by that concentration to get the volume in mL. Multiply the mL by 100 to get units on a U-100 insulin syringe. Example: 5 mg in 2 mL is 2,500 mcg/mL, so 250 mcg is 0.1 mL, or 10 units.
What is a peptide calculator?
A peptide calculator converts three numbers from your vial and plan (the peptide amount, the diluent volume and the dose) into the volume and syringe units to draw. It does unit arithmetic only. It does not decide what dose is right for you.
How many units is 250 mcg of peptide?
It depends on the concentration. At 2,500 mcg/mL (5 mg in 2 mL) 250 mcg is 10 units. At 5,000 mcg/mL (5 mg in 1 mL) it is 5 units. At 2,000 mcg/mL (10 mg in 5 mL) it is 12.5 units. Enter your own vial and water in the calculator to get the exact number.
How much bacteriostatic water should I add to a peptide vial?
There is no single right volume. More water lowers the concentration, so each dose takes up more units and is easier to measure. Less water keeps doses small. Most people pick a volume that puts one dose on a whole-unit mark and fits the vial, often 1–3 mL. The BAC water calculator works this out for a target number of units.
Does the amount of water change the dose?
No. Water changes the concentration, not the total peptide in the vial. If you add more water, you draw more units for the same dose. The mcg you inject stays the same as long as you recalculate.
What is the difference between U-100 and U-40 syringes?
A U-100 syringe is marked for 100 units per mL, so 1 unit is 0.01 mL. A U-40 syringe is marked for 40 units per mL, so 1 unit is 0.025 mL. Drawing a U-100 unit count in a U-40 syringe delivers 2.5 times the intended volume. Peptide and GLP-1 instructions written in units assume U-100.
How many mcg are in 1 mg?
1 mg equals 1,000 mcg (micrograms). So 0.25 mg is 250 mcg and 2.5 mg is 2,500 mcg. The mcg to mg converter handles any value.
How long does a reconstituted peptide last?
It depends on the product. Follow the manufacturer’s instructions first. For compounded multiple-dose vials without specific data, USP Chapter <797> sets a default beyond-use date of 28 days after the vial is first punctured, stored as labelled. The doses per vial calculator checks whether you will finish the vial in time.
Is this peptide calculator medical advice?
No. PeptideConvert performs arithmetic and shows the formula so you can check it. It does not recommend any peptide or dose. Many peptides discussed online are not approved drugs. Always follow your prescription label and your clinician.
Sources and review
The PeptideConvert Editorial Team checks every formula against primary sources and re-reviews pages when labels or guidance change. Read our editorial policy and medical disclaimer.
Get the exact number in seconds
Enter your vial, water and dose. See the units, the math and any warnings instantly.