How do I work out how many doses are in a vial?

Divide the volume of bacteriostatic water you added by the volume per dose. The calculator on this page does it for you: enter the vial size, bac water, and target dose, and the 'Doses per vial' row updates live.

What's the difference between bacteriostatic water and sterile water?

Bacteriostatic water contains a small amount of benzyl alcohol (typically 0.9%) that prevents bacterial growth, so a reconstituted vial keeps for weeks in the fridge. Plain sterile water has no preservative, so a reconstituted vial should be used within a day or two. For multi-dose peptide vials, bacteriostatic water is the usual choice.

Can I use less bac water to make the concentration stronger?

Yes, less water gives a higher concentration and a smaller volume per dose. That can be useful if your dose would otherwise be awkwardly small to draw, but very small volumes are harder to measure precisely on an insulin syringe. Most people aim for a dose volume between 0.05 and 0.2 ml.

What happens if I use the wrong amount of bac water?

Nothing dangerous, but your dose volume changes. If you added twice as much water as you meant to, each draw delivers half the dose. Recalculate using the actual volume you added and adjust the draw, or note the new concentration so future draws match the dose you want.

How long does a reconstituted vial last in the fridge?

Most peptides are stable for around 28 to 30 days reconstituted with bacteriostatic water and kept refrigerated. Some peptides last longer, some shorter. Check the Peptly library entry for your specific peptide for a per-compound estimate.

How do I draw a precise dose on an insulin syringe?

Insulin syringes are marked in units rather than millilitres. On a standard U-100 syringe, 100 units equals 1 ml, so 10 units equals 0.1 ml. The calculator shows the exact unit mark to draw to. Pull slowly, tap out bubbles, and read the meniscus at eye level.

Are these calculations the same for all peptides?

The maths is identical for any powdered peptide that you reconstitute with bacteriostatic water. The only thing that changes is the typical dose and the recommended vial size. The IU input is an approximation suited to peptides where one unit roughly equals one microgram; some peptides use a peptide-specific IU conversion, in which case enter the dose in mcg or mg instead.

Can I track this in an app?

Yes. Peptly tracks your vials, doses, and reconstitution maths automatically. Each vial gets its own page with the live concentration and remaining doses. The free tier covers one protocol.

Is Peptly free to use?

Peptly is free for one protocol with no card required. Paid plans add multiple protocols, deeper insights, and cycle history.

Where can I learn more about specific peptides?

The Peptly library has detail pages for over 100 peptides, including typical doses, half lives, evidence levels, and reconstitution defaults.

Peptide reconstitution calculator

Work out concentration, dose volume, and how many doses you'll get from a vial. Free, no signup needed.

Built for UK + US unitsNo data savedWorks offline

Peptide (optional)

Don't see yours? Use the manual inputs below.

Vial size (mg)

Bacteriostatic water (ml)

I have a larger vial (raises cap to 5 ml)

Target dose per use

Dosing frequency (optional)

Cost of vial (optional)

Results

Concentration

2.50mg/ml

Volume per dose

0.100ml

Insulin syringe

10units

(U-100 / 100u per ml)

Doses per vial

20doses

Draw to this mark:

Fill shown up to 10 units on a U-100 (100 unit) insulin syringe.

Background

FAQ

Track this for real

Save your vials, log doses, and let Peptly do the maths automatically. Free for one protocol, no card needed.