Peptide Calculator
Work out reconstitution concentration, draw volume and insulin-syringe units for any lyophilised research peptide. Free, no sign-up, works offline once loaded.
Reconstitution & draw volume
For laboratory research use only. This tool performs unit conversion for measuring reconstituted material in a research setting. It is not medical guidance and does not recommend any quantity for human use.
How peptide reconstitution works
A lyophilised research peptide arrives as a dry powder under vacuum. Adding bacteriostatic water dissolves it into a solution of known concentration, which is what makes accurate measurement possible. The arithmetic is simple, but it trips people up because three different units are involved at once: milligrams in the vial, millilitres of solvent, and units on an insulin syringe.
The relationship is:
Concentration (mg/ml) = peptide in vial (mg) ÷ bacteriostatic water added (ml)
Everything else follows from that. The volume you need is the amount you want divided by the concentration, and the unit marking is that volume multiplied by 100 — because every insulin syringe, whether U-30, U-50 or U-100, is graduated at 100 units per millilitre. Only the total capacity differs.
Common vial and water combinations
These are the concentrations produced by combinations people ask about most. Use the calculator above for anything not listed.
| Vial | Bacteriostatic water | Concentration | 1 unit (U-100) equals |
|---|---|---|---|
| 5 mg | 2 ml | 2.5 mg/ml | 25 mcg |
| 10 mg | 1 ml | 10 mg/ml | 100 mcg |
| 10 mg | 2 ml | 5 mg/ml | 50 mcg |
| 10 mg | 3 ml | 3.33 mg/ml | 33.3 mcg |
| 15 mg | 3 ml | 5 mg/ml | 50 mcg |
| 30 mg | 3 ml | 10 mg/ml | 100 mcg |
| 50 mg | 5 ml | 10 mg/ml | 100 mcg |
| 100 mg | 5 ml | 20 mg/ml | 200 mcg |
Converting milligrams to insulin units
This is the step that causes the most confusion. A “unit” is a volume marking, not a mass — so the same unit marking represents a different mass depending on how much water went into the vial.
At 100 units per millilitre, the conversion is:
Units = (amount in mg ÷ concentration in mg/ml) × 100
Reconstitute 10 mg in 2 ml and you have 5 mg/ml. Measuring 0.5 mg means 0.1 ml, which is 10 units. Put the same 10 mg into 1 ml instead and the concentration doubles to 10 mg/ml, so the same 0.5 mg is now only 5 units. Nothing about the peptide changed — only the dilution.
Choosing how much water to add
More water gives finer resolution on the syringe and less measurement error, at the cost of using more vial volume per draw. Less water concentrates the solution, which is easier to store but makes small amounts hard to measure accurately.
A practical target is a concentration where a typical measurement falls between 10 and 50 units. Below about 5 units the graduations are too coarse to be precise; above the syringe capacity you need multiple fills. The calculator flags both cases automatically.
Bacteriostatic water vs sterile water
Bacteriostatic water contains 0.9% benzyl alcohol, which suppresses bacterial growth and allows a vial to be entered repeatedly over a period of weeks. Sterile water contains no preservative and is intended for single use — once the seal is broken there is nothing preventing contamination.
For any vial that will be accessed more than once, bacteriostatic water is the appropriate solvent.
Storage after reconstitution
Lyophilised powder is stable at −20 °C and should be protected from light. Once reconstituted, peptides are in solution and considerably less stable — refrigeration at 2–8 °C is standard, and reconstituted material has a materially shorter usable life than the dry powder.
Avoid repeated freeze–thaw cycles of reconstituted solution. Add the solvent slowly against the inside wall of the vial rather than directly onto the powder cake, and swirl rather than shake; peptides are sensitive to mechanical stress and foaming indicates denaturation.
Frequently asked
How much bacteriostatic water should I add to a 10 mg vial?
There is no single correct answer — it depends on the concentration you want. 1 ml gives 10 mg/ml, 2 ml gives 5 mg/ml, 3 ml gives 3.33 mg/ml. Pick the one that puts your intended measurement in a comfortable range on the syringe, and use the calculator above to check.
How many units is 2.5 mg?
Only answerable once concentration is known. At 10 mg/ml, 2.5 mg is 0.25 ml, which is 25 units. At 5 mg/ml the same mass is 0.5 ml, or 50 units — exceeding a U-30 or U-50 syringe.
Does the syringe size change the conversion?
No. U-30, U-50 and U-100 syringes are all graduated at 100 units per millilitre. They differ only in total capacity, which determines whether a given volume fits in one draw.
Can I use the calculator offline?
Yes. The arithmetic runs entirely in your browser with no server calls, so once the page has loaded it continues to work without a connection.
For laboratory research use only. The information on this page describes concentration arithmetic for handling research materials. It is not medical guidance, and nothing here constitutes a recommendation of any quantity for human use.