Free tool

Peptide Reconstitution Calculator

Concentration is the vial content divided by the bacteriostatic water; units to draw are your dose divided by that concentration, times your syringe's units per ml (100 on a U-100). This tool does it for you, entirely in your browser.

This calculator runs entirely in your browser. Nothing you type is sent anywhere. It makes no network requests, sets no cookies, and saves nothing.

Vial amount (mg)

Bacteriostatic water (ml)

Desired dose

Syringe

CoA measured amount (mg, optional)

Purity (%, optional)

Reverse

The three formulas

Reconstitution is three steps. Written out, with no calculator involved:

Concentration = vial content divided by the volume of bacteriostatic water, in mg per ml.
Volume to draw = your dose in mg divided by the concentration, in ml.
Units to draw = the volume to draw multiplied by the units per ml of your syringe.

Which amount counts as the vial content

The first formula needs one number that is not always the number printed on the label. The order of precedence is fixed:

A measured amount from a certificate of analysis is used exactly as entered.
Otherwise, if a purity is given, the content is the label amount multiplied by that purity.
Otherwise the label amount is all there is.

A measured amount is never also multiplied by purity. Doing both discounts the same amount twice and understates the vial.

Running the formulas backwards

The same relation solves in two other directions, which is what the reverse options above do.

From units to dose. If you already drew a number of units and want to know what dose that was, the volume is the units divided by the units per ml, and the dose is that volume multiplied by the concentration.
From a target reading to a water volume. To make a particular dose land on a round number of units, rearrange to water = units multiplied by vial content, divided by dose multiplied by units per ml. That tells you how much bacteriostatic water to add before you mix, rather than after.

Worked backwards: to make a 250 mcg dose read as exactly 5 units on a U-100 syringe from a vial holding 9.75 mg, add 5 times 9.75 divided by 0.25 times 100 = 1.95 ml of water.

A worked example

A 10 mg vial, 2 ml of bacteriostatic water, a 250 mcg dose, a stated purity of 97.5 percent, and a U-100 syringe.

No certificate amount is given, so the content is the label times the purity: 10 mg times 0.975 = 9.75 mg.
Concentration is 9.75 mg divided by 2 ml = 4.875 mg/ml.
The dose of 250 mcg is 0.25 mg. Volume to draw is 0.25 divided by 4.875 = 0.0513 ml.
On a U-100 syringe that is 0.0513 times 100 = 5.13 units, which is the 5.1 quoted elsewhere on this site rounded to one decimal place.
The vial holds 9.75 mg divided by 0.25 mg = 39 doses.

Units per dose by vial size (U-100 syringe)

The same formulas, worked for common vial sizes and water volumes, using the label amount with no purity adjustment. The three dose columns give units to draw on a U-100 syringe, rounded to one decimal place. Adding more water lowers the concentration and raises the units for the same dose, but never changes how many doses the vial holds.

Vial	Water	mg/ml	250 mcg	500 mcg	1 mg	Doses at 250 mcg
5 mg	1 ml	5	5	10	20	20
5 mg	2 ml	2.5	10	20	40	20
5 mg	3 ml	1.7	15	30	60	20
10 mg	1 ml	10	2.5	5	10	40
10 mg	2 ml	5	5	10	20	40
10 mg	3 ml	3.3	7.5	15	30	40
15 mg	1 ml	15	1.7	3.3	6.7	60
15 mg	2 ml	7.5	3.3	6.7	13.3	60
15 mg	3 ml	5	5	10	20	60
20 mg	1 ml	20	1.3	2.5	5	80
20 mg	2 ml	10	2.5	5	10	80
20 mg	3 ml	6.7	3.8	7.5	15	80

On a U-50 syringe, halve every unit figure above; on a U-40, multiply by 0.4; on a U-30, multiply by 0.3.

Reading units on a syringe

Syringe markings are units, not millilitres, and the conversion depends on which syringe you own. A U-100 syringe has 100 units per ml, so one unit is 0.01 ml. A U-50 has 50 units per ml and a U-40 has 40, so the same volume reads as a different number on each. This is why a dose must always be converted against the syringe actually in your hand, and why the syringe selector above changes the answer.

A longer written explanation is published alongside this tool in the articles.

FAQ

What is a peptide reconstitution calculator?

A peptide reconstitution calculator converts a vial amount and a volume of bacteriostatic water into a concentration, then converts your dose into the number of units to draw on your syringe.

How do I calculate units on an insulin syringe?

Divide your dose by the concentration to get a volume in millilitres, then multiply that volume by the units per millilitre of your syringe: 100 for U-100, 50 for U-50, 40 for U-40, 30 for U-30.

What happens if my vial has a certificate of analysis?

A measured amount from a certificate is used exactly as entered. It is never also multiplied by a stated purity, because that would discount the same amount twice and understate what the vial holds.

How does purity change the calculation?

When no measured amount is given but a purity is, the content is the label amount multiplied by the purity. A 10 mg vial at 97.5 percent purity is treated as holding 9.75 mg.

Is anything I type into this calculator sent anywhere?

No. The calculator runs entirely in your browser. It makes no network requests, sets no cookies, and stores nothing, so the numbers you enter never leave your device.

By compound

The same calculator, with a worked example and a doses-per-vial table for one compound:

Using a ready-to-use vial such as Zepbound? See the vial guide.