Reconstitution Math, Without the Hand-Waving

Most reconstitution charts you'll find somewhere are just a table of numbers, with no indication as to how they were arrived at. This is backwards - the arithmetic is simple enough that anyone can do it, and once you can do it you don't need to take anyone else's word for it.

This page is arithmetic, and only arithmetic. It deliberately contains no doses, no suggestions, nothing about what to put in your body. It answers a very narrow question: given a vial of powder and a certain amount of water, what's the concentration, and how much of that is in a syringe?

The whole thing in one line

Reconstitution is dilution, and dilution is division.

Concentration = amount in the vial ÷ volume of water added.

That's it. Everything below is this simple math.

A 10mg vial reconstituted with 2mL of bacteriostatic water is 10 ÷ 2 = 5mg/mL. There is no second step and no hidden factors. The volume of the powder is considered negligible, and that's why nobody cares about it.

Units are where people go wrong

There are two different "units" and they have nothing to do with each other.

Milligrams and micrograms are measures of mass. 1mg = 1,000mcg. This is the conversion that causes real trouble, because it's easy to make a typo or a visual mistake when reading numbers.

Syringe units are volume. On a standard U-100 insulin syringe, 100 units = 1mL. This means that 10 units = 0.1mL, always, regardless of what's in the syringe.

0.1 mL · 0–25 units

0–25 units

25–50

50–100

01 mL

10 units is 0.1mL. The syringe measures volume - it has no idea what's in it. This is the whole point of the arithmetic.

A syringe cannot tell you how much of anything you have. It tells you a volume, and the mass depends entirely on the concentration you created.

Volume to syringe units

Volume	Insulin syringe units
0.05 mL	5 units
0.1 mL	10 units
0.2 mL	20 units
0.25 mL	25 units
0.5 mL	50 units
1.0 mL	100 units

Common vial and water combinations

Each row is simply (amount in vial ÷ water volume) × 0.1mL to get per-10-unit amounts. Check any of them for yourself.

Vial	Water added	Concentration	Per 10 units (0.1 mL)
5 mg	1 mL	5 mg/mL	500 mcg
5 mg	2 mL	2.5 mg/mL	250 mcg
10 mg	1 mL	10 mg/mL	1,000 mcg (1 mg)
10 mg	2 mL	5 mg/mL	500 mcg
50 mg	2 mL	25 mg/mL	2.5 mg
200 mg	2 mL	100 mg/mL	10 mg
500 mg	5 mL	100 mg/mL	10 mg

Note that rows 4 and 1 have the same amount per unit, just different starting vials. It's the concentration that determines your dose, not the vial.

Working it backwards

Going from a target amount to syringe units is the same division, just in the other direction.

Units = (target mass ÷ concentration) × 100

Say you have a 10mg vial reconstituted with 2mL, so 5mg/mL, and you want 250mcg.

Convert to matching units first: 250mcg is 0.25mg. Then 0.25 ÷ 5 = 0.05mL. Multiply by 100 and you get 5 units.

The step people forget is the first one. Dividing 250 by 5 without converting to mg would give you 50 units - ten times too much, from a simple unit mistake.

More water is not weaker, it is easier to measure

A common mistake is to think that adding more water makes the solution weaker. It doesn't - it makes it more dilute, but the amount of substance is the same. The same 10mg vial has 10mg of peptide regardless of how much water you add.

What you do by adding more water is make it easier to measure a small amount. With 1mL, a target of 250mcg is 2.5 units - a fraction you can't really measure on the syringe. With 3mL, the same target is 7.5 units, which is right between two marks. With 2mL it's 5 units, which is a whole number.

Dilute to make your target amount land on a mark you can actually measure. That's the only reason to pick one volume of water over another.

Storage

These are facts, not suggestions:

Lyophilized (freeze-dried) powder is stable at refrigerator temperatures and generally tolerant of shipping at room temperature. Once reconstituted, solutions are stored in the refrigerator, not the freezer.

Bacteriostatic water contains benzyl alcohol, which inhibits bacterial growth. Sterile water does not, and the two are not interchangeable once a vial is opened more than once.

When adding water to a vial, do so down the side rather than directly onto the powder. Peptides are fragile in a mechanical sense - shaking or vigorous movement can damage them.

What this math doesn't tell you

The arithmetic is simple, but everything it's built on may not be.

It assumes that the vial actually contains what it's supposed to. This is an assumption about the manufacturer, not the chemistry, and it's the only factor that can make all of this math incorrect. A purity or fill-weight issue would make every calculation on this page wrong in a way no amount of careful division will fix.

It doesn't say anything about whether a particular amount is appropriate, safe, or effective for any reason. Those are entirely separate discussions, and the confidence with which a dosing chart presents numbers has a way of making people think that the chart answers those questions, too.

A number being calculable is not evidence that it's a good idea.

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This page only discusses dilution arithmetic. It is not medical advice, and it is not a recommendation to use any particular substance. Nothing on this page has been evaluated by the FDA.