How much bacteriostatic water for a 5 mg P21 vial?

The amount of water does not change how much P21 is in the vial; it sets the concentration. With 1 mL a 5 mg vial is 5 mg/mL, with 2 mL it is 2.5 mg/mL and with 3 mL it is 1.667 mg/mL. More water makes each unit weaker, so a given amount takes more units to draw.

How many mcg are in one unit of a 5 mg P21 vial?

With 2 mL of water, one unit on a U-100 syringe holds 25 mcg (2,500 mcg per mL divided by 100). The table above gives the figure for other vial sizes and volumes.

Is this a P21 dosage calculator?

It converts between amounts, volumes and syringe units for P21; it does not suggest how much to use. The P21 guide lists the doses used in published studies, with their sources.

What size are P21 vials?

Across 82 listings in our directory, the most common sizes are 5 mg, 10 mg, 2 mg, 100 mg. Sizes and prices by store are on the P21 price page.

How many units are in 1 mL on an insulin syringe?

A U-100 insulin syringe holds 100 units per mL, so 1 unit is 0.01 mL.

Tool · P21 reconstitution arithmetic

P21 dosage calculator

Pick a P21 vial size, enter the bacteriostatic water added and, if you want, an amount per draw. The calculator gives the concentration and how many units that is on a U-100 insulin syringe. It does arithmetic only and does not suggest an amount.

U-100 syringes · 100 units = 1 mL · 1 mg = 1,000 mcg

Concentration

2.5 mg/mL

25 mcg per unit on a U-100 syringe · 250 mcg per 0.1 mL

Enter an amount per draw to see how many units it is and how many draws the vial holds.

Not medical advice

This tool converts between amounts, volumes and syringe units. It is not a recommendation to use P21 or a guide to how much to use, and it cannot tell you whether a product is what its label says. For the amounts used in research, with sources, see the doses used in published P21 studies. Disclaimer

P21 vial sizes stores list

From 82 active P21 listings of 100 mg or less in our directory. The buttons above use these sizes.

5 mg31 listings
10 mg24 listings
2 mg9 listings
100 mg7 listings
50 mg6 listings
20 mg2 listings

Compare P21 prices by supplier

Worked example

A 5 mg P21 vial with 2 mL of bacteriostatic water is 2.5 mg/mL (2,500 mcg/mL). One unit on a U-100 syringe is 0.01 mL, so each unit holds 25 mcg. To find how many units an amount is, divide the amount in mcg by 25.

Read more about bacteriostatic water and storing a mixed vial, or the P21 guide.

P21 concentration by vial size and water added

mcg per unit on a U-100 syringe. Read across for more water, down for a larger vial.

Vial	1 mL water	2 mL water	3 mL water
2 mg	20 mcg/unit · 2 mg/mL	10 mcg/unit · 1 mg/mL	6.7 mcg/unit · 0.67 mg/mL
5 mg	50 mcg/unit · 5 mg/mL	25 mcg/unit · 2.5 mg/mL	16.7 mcg/unit · 1.67 mg/mL
10 mg	100 mcg/unit · 10 mg/mL	50 mcg/unit · 5 mg/mL	33.3 mcg/unit · 3.33 mg/mL
20 mg	200 mcg/unit · 20 mg/mL	100 mcg/unit · 10 mg/mL	66.7 mcg/unit · 6.67 mg/mL
50 mg	500 mcg/unit · 50 mg/mL	250 mcg/unit · 25 mg/mL	166.7 mcg/unit · 16.67 mg/mL
100 mg	1,000 mcg/unit · 100 mg/mL	500 mcg/unit · 50 mg/mL	333.3 mcg/unit · 33.33 mg/mL

Questions

How much bacteriostatic water for a 5 mg P21 vial?: The amount of water does not change how much P21 is in the vial; it sets the concentration. With 1 mL a 5 mg vial is 5 mg/mL, with 2 mL it is 2.5 mg/mL and with 3 mL it is 1.667 mg/mL. More water makes each unit weaker, so a given amount takes more units to draw.
How many mcg are in one unit of a 5 mg P21 vial?: With 2 mL of water, one unit on a U-100 syringe holds 25 mcg (2,500 mcg per mL divided by 100). The table above gives the figure for other vial sizes and volumes.
Is this a P21 dosage calculator?: It converts between amounts, volumes and syringe units for P21; it does not suggest how much to use. The P21 guide lists the doses used in published studies, with their sources.
What size are P21 vials?: Across 82 listings in our directory, the most common sizes are 5 mg, 10 mg, 2 mg, 100 mg. Sizes and prices by store are on the P21 price page.
How many units are in 1 mL on an insulin syringe?: A U-100 insulin syringe holds 100 units per mL, so 1 unit is 0.01 mL.

Working with a different product? Use the general peptide calculator.