Peptides ship as a lyophilised powder. Once solvent is added you need to know the resulting concentration, and how much solution corresponds to a given mass of peptide. This does that arithmetic. It is a unit converter, nothing more.
Printed on the vial. A "10mg" vial contains 10mg of dry powder.
More water means a weaker mix and a bigger volume to draw. It does not change how much peptide you get. 1mL, 2mL, and 3mL are the usual choices.
The mass of peptide you want in a single measured volume. This tool does not suggest a value and we do not supply one.
Standard U-100 insulin syringes. On all three, 100 units equals 1mL.
Used only to estimate how long a vial lasts.
Check the result against the vial strength and solvent volume before you rely on it. A misplaced decimal is by far the most common error here, and it is silent: the arithmetic looks fine, the number is just wrong by a factor of ten.
Your vial holds a fixed amount of peptide. Adding water does not add or remove any peptide, it just spreads the same amount through more or less liquid.
So if you put 2mL of water into a 10mg vial, every 1mL of that liquid holds 5mg. To take a 300mcg dose, you need 0.06mL, which is 6 units on a U-100 insulin syringe.
Use less water and the mix gets stronger, so you draw a smaller amount. Use more water and it gets weaker, so you draw more. Same dose either way.
"Units" on an insulin syringe are not a dose. They are a volume measurement. 100 units equals 1mL of liquid, whatever is in it. If someone online tells you to take "10 units" of a peptide, that instruction is meaningless without knowing how their vial was mixed. Their 10 units and your 10 units can be completely different amounts of drug.
This is why we do not publish quantity charts. The same mass of peptide is a different volume in every vial, depending on how much solvent was added, so a chart that ignores that is wrong more often than it is right.
Whatever suits the measurement you need. More solvent makes small doses easier to measure accurately, because you are drawing a bigger and more readable volume. Very small draws on a syringe are hard to get right.
Use what you were given. Bacteriostatic water contains a preservative that lets a vial be punctured more than once. Sterile water has no preservative and is generally single use. Never use tap or bottled water.
Refrigerated, and follow the beyond-use date your pharmacy puts on it. That date is not a suggestion. Do not freeze it, and do not shake it hard when mixing. Aim the water at the side of the vial and let it dissolve by itself.
Do not eyeball it. Use less solvent so the volume lands somewhere you can actually read on the barrel.
The arithmetic is the same for anything supplied as a powder measured in mg or mcg. It does not apply to products dosed in IU, such as HCG or HGH, because IU is a measure of biological activity rather than weight and does not convert cleanly.