Peptide Reconstitution Calculator

Stop guessing how much water to add

Most people reconstitute backwards. They pick a bacteriostatic water volume because it's what someone on a forum used, mix the vial, and only then work out what a dose looks like on the syringe — and end up with an awkward draw like 7.3 units sitting between two gridlines. Every injection after that is an estimate.

The water volume is the one variable you fully control, and it's the one that decides how readable every future draw is. So it should be the output, not the input. Enter the dose you actually want, and the calculator above returns the water volume that puts that dose on a mark you can see.

How the calculator picks your water volume

A U-100 insulin syringe is labeled every 10 units. Those gridlines are the only marks most people can read reliably at a glance, so the planner treats them as the target rather than an accident:

For each 10-unit mark — 10, 20, 30, up to 100 — it derives the concentration that would land your dose exactly on that mark.
It converts each concentration back to a bacteriostatic water volume, and discards anything that doesn't fit a real vial: under 0.5 mL, over 5 mL, or above 50 mg/mL, which is more than most lyophilized peptides will readily dissolve into.
It ranks what's left. Water volumes that themselves land on a syringe mark come first, because you measure the bac water with the same syringe — 2.0 mL is easy, 0.72 mL is not. Then it favours a comfortable draw size: 10–30 units is the sweet spot for a peptide dose, 40 is fine, and anything above that is workable but larger than it needs to be.

What you get back is the top plan plus the alternates, so if you'd rather draw 20 units than 10, that option is right there with its own water volume.

Peptide reconstitution chart — common vial sizes and doses

Every row below is the calculator's top pick for that combination, so you can look up a common protocol without entering anything. All figures assume a U-100 insulin syringe, where 1 mL is 100 units.

Bacteriostatic water volume, concentration, syringe units, and doses per vial for common peptide vial sizes and doses
Vial size	Dose per injection	Add BAC water	Concentration	Draw (U-100)	Doses per vial
2 mg	100 mcg	2 mL	1 mg/mL	10 units	20
	200 mcg	1 mL	2 mg/mL	10 units	10
	250 mcg	0.8 mL	2.5 mg/mL	10 units	8
	500 mcg	0.8 mL	2.5 mg/mL	20 units	4
5 mg	100 mcg	5 mL	1 mg/mL	10 units	50
	250 mcg	2 mL	2.5 mg/mL	10 units	20
	500 mcg	1 mL	5 mg/mL	10 units	10
	1 mg	0.5 mL	10 mg/mL	10 units	5
10 mg	250 mcg	4 mL	2.5 mg/mL	10 units	40
	500 mcg	2 mL	5 mg/mL	10 units	20
	1 mg	1 mL	10 mg/mL	10 units	10
	2 mg	0.5 mL	20 mg/mL	10 units	5
15 mg	500 mcg	3 mL	5 mg/mL	10 units	30
	1 mg	1.5 mL	10 mg/mL	10 units	15
	2.5 mg	0.6 mL	25 mg/mL	10 units	6
30 mg	1 mg	3 mL	10 mg/mL	10 units	30
	2 mg	1.5 mL	20 mg/mL	10 units	15
	5 mg	0.6 mL	50 mg/mL	10 units	6

Scroll the table sideways to see every column.

The draw column is 10 units on almost every row, and that isn't a coincidence — it's the whole point. The planner picks the water volume that puts your dose on a labeled gridline, so the number you read off the barrel stays the same easy one while the water volume absorbs the difference between protocols. The exception is the 2 mg vial at 500 mcg, where a 10-unit draw would need less water than you can measure accurately, so it lands on 20 units instead.

One thing the chart can't know is your vial's capacity. A few rows call for a large fill — 5 mL into a 5 mg vial for 100 mcg dosing, for instance — and a typical 3 mL vial physically won't take it. When the top pick overfills your vial, use one of the alternates the calculator lists above; each one is a clean mark too, just at a different draw size.

The math, if you want to check it

Three lines, and the calculator is just doing them in the other direction:

Concentration = peptide in the vial (mg) ÷ bacteriostatic water added (mL)
Volume to draw = your dose (mg) ÷ concentration (mg/mL)
Syringe units = volume to draw (mL) × 100 on a U-100 syringe

Worked through: 2 mL of bacteriostatic water into a 5 mg vial gives 2.5 mg/mL. A 250 mcg dose is 0.25 mg, so 0.25 ÷ 2.5 = 0.1 mL — which is 10 units on a U-100 syringe, right on a labeled mark. Solving it forwards means checking whether you got lucky. Solving it backwards means you always do. There's a fuller walkthrough with more compounds in our guide to calculating peptide reconstitution in insulin-syringe units.

It remembers the vial so you don't have to

A calculator gets you the right ratio once. The problem starts three weeks later, when you're trying to remember your own math and how much is actually left in the vial.

Dose Track tracks the active amount remaining in each vial after every logged draw. It knows what's left, flags the vial when it's running low or nearing its stability window, and tells you it's time to mix the next one — so you reconstitute ahead of time instead of finding out mid-protocol. Confirm a plan from the calculator in the app and the ratio is saved: every future dose is already converted to units for you, for any vial size and any of the 600+ compounds it supports.

How it works — 3 steps

Enter your vial size and your dose. The peptide amount in milligrams is on the vial label. The dose is whatever your protocol calls for, in mcg or mg. You don't need a water volume — that's the answer.
Add the water it gives you. Run it slowly down the side of the vial and swirl to dissolve; don't shake. The calculator's volume is the one that lands your dose on a clean mark.
Draw and log. Pull to the unit mark shown. Log the draw so the vial's remaining amount stays current and you get the warning before you run out.

More than a one-time calculation

Reconstitution is the first thing a peptide protocol asks of you, not the last. Dose Track keeps the rest of it straight: every draw logged, injection sites rotated automatically, and your actual plasma levels modeled against each compound's half-life and Tmax — so you can see whether you're holding steady state rather than assuming it. More on that in the peptide tracking guide.

Frequently asked questions

How much bacteriostatic water should I add to a peptide vial?+

It depends on the dose you want per injection, not on a fixed rule. Rather than picking a water volume and doing the math after, work backwards: enter your vial size and target dose, and the calculator returns the water volume that lands that dose on a clean insulin-syringe mark. For a 5 mg vial dosed at 250 mcg, that is 2 mL.

How do I calculate peptide dosage in units on an insulin syringe?+

Divide the peptide amount in the vial by the bacteriostatic water volume to get concentration in mg/mL, then divide your dose by that concentration to get the volume to draw in mL. On a U-100 syringe, 1 mL is 100 units, so multiply by 100. Example: 5 mg in 2 mL is 2.5 mg/mL, so 250 mcg is 0.1 mL, or 10 units.

Does adding more bacteriostatic water make a peptide weaker?+

No. It lowers the concentration per millilitre, but the total peptide in the vial is unchanged — the same milligrams are simply spread across more liquid, so each dose is a larger draw. More water means more syringe units per dose and finer control on small doses; less water means fewer units and a smaller, harder-to-read draw.

What if my dose doesn't land on a clean syringe mark?+

A draw like 7.3 or 23 units sits between the labeled 10-unit gridlines on a U-100 syringe and reads poorly, which is where dosing error creeps in. Changing the water volume changes where the dose lands. This calculator only recommends volumes that put your dose on a clean 10-unit mark.

How do I know when it's time to reconstitute a new vial?+

Dose Track subtracts every logged draw from the vial's remaining volume, so the active amount left is always current. The app warns you when a vial is running low or approaching its expiration window and reminds you to mix the next one ahead of time, instead of finding out mid-protocol.

What if I don't have a U-100 insulin syringe?+

Switch the syringe scale in the calculator. U-100 syringes read 100 units per mL and are the standard for peptide dosing; U-40 syringes read 40 units per mL. The calculator recalculates the recommended water volume and the units to draw against whichever scale you select, so the marks match the barrel in your hand.

Is this peptide reconstitution calculator free?+

Yes. The calculator on this page is free, runs entirely in your browser, and requires no account — nothing you type is sent to a server. The same smart reconstitution planner is built into the Dose Track app for iOS and Android at no cost, where it also tracks each vial's remaining amount.