Tool
Peptide reconstitution calculator: BAC water, concentration and units
Enter the mg of peptide in the vial and the mL of bacteriostatic water you add. The calculator gives the concentration, the volume and units to draw for a dose on an insulin syringe, and the doses in the vial.
Guides:how much water to add·the maths·how to reconstitute·bac water·printable chart
Your vial
Printed on the vial. There is no standard size - enter what yours says.
This changes how much you draw - never how many doses the vial holds.
100 units per mL. 1 unit = 0.01 mL. This is what almost every insulin syringe sold is, in every barrel size.
Capacity only. A 1 mL U-100 syringe holds 100 units - the scale decides that, not the barrel.
Draw this much
= 0.1 mL on a 1 mL U-100 syringe
- Concentration
- 2,500 mcg/mL
- Exact volume
- 0.1 mL
- Dose you actually get
- 250 mcg
- Doses per vial(unaffected by water volume)
- 20
Results update in the address bar, so you can copy the link to save or share a calculation. Nothing is stored, and there is no account.
How much bacteriostatic water to add
There is no single correct amount. Mixing a peptide comes down to choosing a water volume, and that choice sets the concentration. The concentration then sets how many syringe units each dose takes up.
The water never changes how many doses the vial holds. A 5 mg vial holds 5,000 mcg whatever you add, so it holds 20 doses of 250 mcg with 1, 2 or 3 mL. The tables below show how the units per dose change with the water.
5 mg vial: units per dose by water volume
| Water added | Concentration | 1 unit = | 100 mcg | 250 mcg | 500 mcg |
|---|---|---|---|---|---|
| 1 mL water | 5 mg/mL | 50 mcg | 2 units | 5 units | 10 units |
| 2 mL water | 2.5 mg/mL | 25 mcg | 4 units | 10 units | 20 units |
| 3 mL water | 1.67 mg/mL | 16.67 mcg | 6 units | 15 units | 30 units |
Units on a U-100 insulin syringe (100 units = 1 mL), to the nearest half unit. Example doses only, not a recommendation.
10 mg vial: units per dose by water volume
| Water added | Concentration | 1 unit = | 250 mcg | 500 mcg | 1 mg |
|---|---|---|---|---|---|
| 1 mL water | 10 mg/mL | 100 mcg | 2.5 units | 5 units | 10 units |
| 2 mL water | 5 mg/mL | 50 mcg | 5 units | 10 units | 20 units |
| 3 mL water | 3.33 mg/mL | 33.33 mcg | 7.5 units | 15 units | 30 units |
Units on a U-100 insulin syringe (100 units = 1 mL), to the nearest half unit. Example doses only, not a recommendation.
Choosing a volume
Because the dose count is fixed, the water is chosen for measuring:
- Readable units. More water spreads the same dose across more units, and a dose of 10 units is easier to measure accurately than one of 2.
- Fits the barrel. The draw still has to fit the syringe. A 0.3 mL U-100 barrel holds 30 units, a 0.5 mL barrel 50 and a 1 mL barrel 100. All of them are still 100 units per mL.
- Easy numbers. A volume that gives a round concentration (2,500 mcg/mL rather than about 1,667) makes each result easier to check by hand.
Bacteriostatic water is sterile water with a preservative (benzyl alcohol), so a vial can be entered more than once. Sterile water for injection has none. The bacteriostatic water guide covers the difference, and what vendors sell as reconstitution solution.
How reconstitution maths works
Reconstitution maths is a few divisions and one multiplication, so you can check any calculator's answer by hand. One example runs through every step: a 5 mg vial, 2 mL of bacteriostatic water and a 250 mcg dose, read on a U-100 insulin syringe. It is the example the calculator above opens with.
- Use one unit. Vials are labelled in mg and doses are usually quoted in mcg. 1 mg is 1,000 mcg, so the vial holds 5,000 mcg. Skipping this step is how a 1,000× error happens.
- Concentration. Divide the peptide by the water: 5,000 mcg ÷ 2 mL = 2,500 mcg per mL. This is the only step the water enters.
- Volume to draw. Divide the dose by the concentration: 250 ÷ 2,500 = 0.1 mL.
- Syringe units. The U-number is units per mL, so on a U-100 syringe multiply by 100: 0.1 mL is 10 units. On a U-40 syringe the same 0.1 mL is 4 units.
- Doses per vial. Divide the peptide by the dose: 5,000 ÷ 250 = 20 doses.
| Step | Formula | Worked example |
|---|---|---|
| Concentration | vial mcg ÷ mL of water | 5,000 ÷ 2 = 2,500 mcg/mL |
| Volume | dose ÷ concentration | 250 ÷ 2,500 = 0.1 mL |
| Units (U-100) | mL × 100 | 0.1 × 100 = 10 units |
| Doses per vial | vial mcg ÷ dose | 5,000 ÷ 250 = 20 |
Printable reconstitution chart
Units per dose for 2, 5 and 10 mg vials at 1, 2 and 3 mL of water, on one page for the fridge. View and print the chart, or have it emailed to you.
Common questions
How much bacteriostatic water do I add to a 5 mg peptide vial?
There is no single correct amount; the tables on this page use 1, 2 and 3 mL. With 2 mL, a 5 mg vial is 2,500 mcg per mL, so 250 mcg is 10 units on a U-100 syringe. With 1 mL the same dose is 5 units, and with 3 mL it is 15 units. The vial holds 20 doses of 250 mcg whichever you choose.
How much bacteriostatic water do I add to a 10 mg vial?
Again there is no single correct amount. With 2 mL, a 10 mg vial is 5,000 mcg per mL, so 500 mcg is 10 units on a U-100 syringe. With 1 mL the same dose is 5 units, and with 3 mL it is 15 units. More water makes small doses easier to measure, as long as the draw fits your syringe.
How do I work out peptide concentration after reconstitution?
Convert the vial to micrograms (mg × 1,000), then divide by the millilitres of water added. A 5 mg vial with 2 mL of water is 5,000 ÷ 2 = 2,500 mcg per mL. The volume to draw, the syringe units and the doses per vial all follow from that number.
How many units is 250 mcg?
It depends on the concentration. From a 5 mg vial mixed with 2 mL of water (2,500 mcg per mL), 250 mcg is 0.1 mL, which is 10 units on a U-100 insulin syringe. From a 10 mg vial with 2 mL (5,000 mcg per mL), the same 250 mcg is 5 units.
Does adding more water give me more doses?
No. The number of doses depends only on the peptide in the vial and the dose size. A 5 mg vial holds 20 doses of 250 mcg with 1 mL, 2 mL or 3 mL of water. More water only makes each dose a larger volume.
What is the difference between bacteriostatic water and sterile water?
Bacteriostatic water is sterile water with benzyl alcohol, typically 0.9%, added as a preservative so a vial can be entered more than once. It is labelled not for use in newborns. Sterile water for injection contains no preservative. The arithmetic on this page is the same with either.
Why do reconstitution calculators give different answers?
The usual causes are treating a "U-50" syringe as 50 units per mL, mixing up mg and mcg, or assuming more water makes more doses. There is no U-50 scale: a 50-unit syringe is a 0.5 mL barrel still marked at 100 units per mL. This calculator asks for scale and barrel size separately for that reason.
Is this the same as the peptide dosage calculator?
It runs the same arithmetic. This page leads with mixing: how much water to add and what concentration it gives. The peptide calculator at /tools/dosage-calculator/ leads with dosing and links to calculators preset for specific peptides.
Is this calculator medical advice?
No. It does arithmetic on the numbers you enter. It does not know what is in your vial or whether any dose is right for you. Many peptides discussed on this site are sold for laboratory research use only and are not approved for human use.