Skip to content
Peptideworth

Calculator

Bacteriostatic Water Calculator

This runs the reconstitution arithmetic backwards. Instead of taking the water you already added and telling you the concentration, it takes the concentration you have chosen and tells you the water to add — and then what one unit on a standard insulin syringe is worth at that concentration, which is the number that decides how finely you can measure anything afterwards. Both figures come from you: this tool never proposes a concentration, and it has no dose to suggest.

By Grant Delaney, Research Editor

This tool does not recommend a dose

It performs arithmetic only. Every quantity it works with is one you type in — nothing is built in, nothing is defaulted, and no field starts with a number already in it. If you have not already settled on the quantities this page asks for, it has nothing to compute for you.

Work it backwards

Calculator

  1. The total milligrams the label states the vial contains. If the vial carries no mass on its label there is no number to enter here, and no arithmetic this page can do.

  2. Stronger means a smaller injection volume; weaker means more syringe units per milligram and an easier barrel to read. This tool has no view on which you should pick — it works out the water for whichever you do.

Enter the mass on your vial and the concentration you have chosen, both greater than zero. The water volume follows from those two numbers and nothing else.

Read this too

What this calculator does not tell you

It does not know your real concentration

The concentration here is a labelled mass divided by the water you say you added — the figure anyone can compute from their own vial. It is not a manufacturer's measured final-volume figure, because dissolved powder takes up space of its own. On the EGRIFTA WR label the diluent added is 1.3 mL, but the label's own dose figures imply a final volume of 1.45 mL, so dividing by the diluent alone overstates concentration by 11.5% on that product. See the full worked example, checked against the label. If you know your product's actual final volume, use that instead.

It does not know your vial will hold that much

The water volume above is arithmetic, not a fit check. A vial has a fixed internal volume and the powder already occupies some of it — if the figure this page returns is larger than the vial can physically take, the vial is the constraint, not the calculation.

It does not know whether a quantity is appropriate

Every equation here takes a quantity as an input and converts it. None of them produces one, and no amount of arithmetic can. What quantity is appropriate for a particular person is a prescribing decision, not a calculation.

It does not verify sterility, purity, or legality

A number coming out of this calculator says nothing about what is actually in a vial, whether it was prepared correctly, or whether the compound is legal for you to obtain.

The arithmetic

How the math works

Two numbers go in: the mass printed on the vial (mg) and the concentration you have decided to mix to (mg/mL).

Water to add = vial strength (mg) ÷ your chosen concentration (mg/mL). That is the whole calculation, and it is the reconstitution calculator's first step solved for the other variable.

What one unit holds = your concentration ÷ 100, because one unit on a U-100 syringe is one hundredth of a millilitre. This is the number that decides how finely you can measure anything afterwards, and it is a property of your solution rather than a judgement about it.

Glossary

Key terms

Bacteriostatic water
Sterile water with a small amount of benzyl alcohol added as a preservative, which lets a multi-dose vial be entered repeatedly rather than used once and discarded.
Concentration (mg/mL)
How much peptide sits in each millilitre of the mixed solution — the exchange rate between a mass and a volume.
Vial strength
The total mass of peptide printed on the vial's label, in milligrams — before any water is added.
Syringe units (U-100)
The markings on a standard U-100 insulin syringe, where 100 units equal 1 millilitre. A different syringe, such as a U-40, uses a different scale entirely.
Resolution
The smallest quantity you can reliably read off a syringe — one unit's worth at your concentration. A finer resolution is not automatically a better one; it is simply a different trade against injection volume.

Before you calculate

Approval status of peptides commonly reconstituted this way

The arithmetic above is identical no matter which peptide is in the vial. What you are legally able to obtain is not — it varies by compound, and it is worth checking before you calculate anything.

Questions

Frequently asked questions

How much bacteriostatic water should I add to my vial?

That is a choice, not a fact, and this tool does not make it for you. Adding more water gives a weaker solution measured in more syringe units, which is easier to read off a barrel accurately; adding less gives a smaller volume to inject. The calculator tells you the water volume that produces whatever concentration you decide on, and shows what one unit is then worth so you can see the trade-off in numbers rather than guess at it.

What does 'one unit is worth X mcg' actually mean?

It is the resolution you are working at. A standard U-100 syringe is marked in units, each one hundredth of a millilitre, and that marking is the smallest quantity you can reliably read. At a strong concentration each of those marks carries a lot of peptide, so a small misread moves a lot; at a weaker one each mark carries less. The figure is a property of your solution and your syringe, not a judgement about either.

Why is the water volume this calculator gives me not the final volume in the vial?

Because dissolved powder occupies space of its own. The volume you end up with is the water you added plus the volume the peptide itself takes up, so the real concentration is slightly weaker than the arithmetic here suggests. On the EGRIFTA WR label, the diluent added is 1.3 mL while the label's own dose figures imply a final volume of 1.45 mL — an 11.5% gap on an approved product. This tool divides by the diluent volume, like every other calculator of its kind, and says so rather than implying a precision it does not have.

Is bacteriostatic water the same as sterile water?

No. Bacteriostatic water contains a small amount of benzyl alcohol as a preservative, which is what allows a vial to be entered repeatedly rather than used once and discarded. Plain sterile water has no preservative. The arithmetic above is identical either way — it is a volume calculation — but which diluent a product calls for is stated by that product, not by this page.

Medical disclaimer: This content is for general educational purposes only and is not medical advice, diagnosis, or treatment. Always consult a licensed healthcare professional before starting, stopping, or changing any treatment.