Peptide calculator
Work out the syringe draw for a dose you’ve been prescribed. Example: 5 mg in 2 mL is 2.5 mg/mL, so a 250 mcg dose is 10 units on a U-100 syringe.
Updated 29 October 2026
Loading calculator…
A note on legality and safety
Most injectable peptides sold online are unlicensed in the UK. This calculator does the maths for a dose you’ve been prescribed; it doesn’t suggest doses or tell you what to take. Always check every number against your prescription label, and check the UK legal status of what you’re using. The maths assumes the vial contains exactly what the label says.
How it works
The whole tool is three small steps of arithmetic:
- strength = vial mg ÷ water mL
- volume mL = dose mg ÷ strength
- units = volume mL × units-per-mL (100 for U-100)
Concentration chart
Strength and “1 unit = ? mcg” for common vial and BAC water combinations (U-100).
| Vial \ BAC water | 1 mL | 2 mL | 2.5 mL | 3 mL |
|---|---|---|---|---|
| 5 mg | 5 mg/mL | 2.5 mg/mL | 2 mg/mL | 1.67 mg/mL |
| 10 mg | 10 mg/mL | 5 mg/mL | 4 mg/mL | 3.33 mg/mL |
| 15 mg | 15 mg/mL | 7.5 mg/mL | 6 mg/mL | 5 mg/mL |
| 20 mg | 20 mg/mL | 10 mg/mL | 8 mg/mL | 6.67 mg/mL |
Syringe reference (U-100)
| Syringe | Capacity | mL per line | Reads well above |
|---|---|---|---|
| 0.3 mL U-100 (30 units) | 30 units | 0.010 mL | 10 units |
| 0.5 mL U-100 (50 units) | 50 units | 0.010 mL | 10 units |
| 1 mL U-100 (100 units) | 100 units | 0.020 mL | 20 units |
| 1 mL U-40 (40 units) | 40 units | 0.025 mL | 10 units |
Common questions
- How many units is 1 mg?
- It depends on the strength. Units = (dose in mg ÷ strength in mg/mL) × 100 on a U-100 syringe. At 5 mg/mL, 1 mg is 20 units. Enter your own strength above to get the exact figure.
- How do I convert units to mg?
- mg = (units ÷ 100) × strength in mg/mL on a U-100 syringe. Use the mg ↔ units tab, set it to “units → dose”.
- How many units are in 1 mL?
- On a U-100 syringe, 1 mL is 100 units, so 1 unit is 0.01 mL. On a U-40 syringe, 1 mL is 40 units.
- Does syringe size change the number of units?
- No, as long as the scale is the same. A 0.3, 0.5 and 1 mL U-100 syringe all give the same units for the same dose. A U-40 syringe is different: the same dose is 2.5 times fewer units.
- How much BAC water (bacteriostatic water) should I add?
- There is no single right answer: more BAC water means a bigger, easier-to-read draw but a weaker strength. Use the “How much water?” tab to see which volumes keep your dose easy to measure on your syringe.
- Why does it say my dose is hard to measure?
- If the draw is only a few units, reading to the nearest line can be off by a large percentage. Adding more BAC water makes the draw bigger, or a syringe with finer markings helps.
- What is the difference between mg and mcg?
- 1 mg = 1000 mcg. Mixing the two up is the most common and most dangerous dosing error, so this calculator flags a dose that looks like it is in the wrong unit.
- How many doses are in my vial?
- Full doses per vial = the vial amount ÷ the dose, rounded down. It is a theoretical maximum: a little liquid is always left in the vial and needle.
- What does mg/mL mean?
- It is the strength, or concentration: how many milligrams of peptide are in each millilitre of liquid after mixing. Strength = vial amount in mg ÷ water in mL.
- What if my dose falls between two lines?
- The calculator shows the nearest printed line and marks the exact draw. If a dose consistently lands between lines, a different water volume can move it onto a line.
- Can I use it for a blend or stack?
- Yes. The Blend / stack tab takes a vial with several peptides; you set the dose on one and it shows how much of each of the others comes along in the same draw.
- Is it legal to buy injectable peptides in the UK?
- Most injectable peptides sold online are unlicensed in the UK. Licensed weight-loss medicines (such as Mounjaro and Wegovy) are prescription-only. This tool does the maths for a dose you have been prescribed; it does not suggest doses or supply.
Related tools
Is it still good?How long a pen or mixed vial keeps, in and out of the fridge.Are peptides legal in the UK?What’s licensed, what isn’t, and what that means for you.
This is a maths tool, not medical advice. It doesn’t recommend a dose, a medicine or a supplier. Report side effects to the MHRA Yellow Card scheme.