Not instructions for useThis page explains the arithmetic of mixing. Which diluent is right, how to keep a vial sterile and how long a mixed vial stays usable are questions for a pharmacist, and for approved medicines the label answers them. Most peptides sold online have no approved label at all.
The three numbers that matter
Every reconstitution problem has the same three inputs and one output:
A U-100 insulin syringe holds 100 units in 1 mL, so one unit is 0.01 mL.[1] The calculator above runs these lines for you. Change only the diluent and you will see the concentration and units move while the amount in the vial stays the same.
How the diluent volume changes the reading
Take a 10 mg vial and an example amount of 100 mcg. The table shows what happens as the volume of liquid goes up.
| Diluent | mg/mL | mcg per unit | Units for 100 mcg |
|---|---|---|---|
| 0.5 mL | 20 | 200 | 0.5 |
| 1 mL | 10 | 100 | 1 |
| 1.5 mL | 6.667 | 66.67 | 1.5 |
| 2 mL | 5 | 50 | 2 |
| 2.5 mL | 4 | 40 | 2.5 |
| 3 mL | 3.333 | 33.33 | 3 |
| 4 mL | 2.5 | 25 | 4 |
| 5 mL | 2 | 20 | 5 |
The units scale in a straight line with the volume: twice the liquid, twice the units. Nothing about the peptide changes. Only the spacing between the amount you want and the next line on the syringe does.
Choosing a volume: the two limits
There is no universally correct amount of liquid. For an unapproved product there is also no label that sets one. The arithmetic still gives two hard limits:
- Too little liquid makes the solution so concentrated that small amounts land on one or two units. On a 1 mL syringe the marks are usually 2 units apart, so a reading of 1 unit is a guess.
- Too much liquid pushes larger amounts past the syringe. A 0.3 mL syringe holds 30 units and a 0.5 mL syringe holds 50.
A simple check: work out the units for the smallest and the largest amount you will ever need to measure from that vial. Both should sit comfortably inside one syringe size.
Diluent volume for a round reading
You can also run the math backwards. Pick the number of units you want a given amount to equal, and solve for the liquid:
| Vial | 10 units = 100 mcg | = 250 mcg | = 500 mcg | = 1,000 mcg |
|---|---|---|---|---|
| 2 mg | 2 mL | 0.8 mL | under 0.5 mL | under 0.5 mL |
| 5 mg | 5 mL | 2 mL | 1 mL | 0.5 mL |
| 10 mg | over 5 mL | 4 mL | 2 mL | 1 mL |
Read a row as: "add this much liquid to this vial, and every 10 units on the syringe will hold that many micrograms." Cells marked over 5 mL or under 0.5 mL are not practical volumes for a small vial.
The table does not know how much liquid your vial can physically hold. Check that before relying on any volume above about 3 mL.
Which liquid: the product label decides
The diluent is set by each product's label, not by the calculator. The two current tesamorelin products show why: Egrifta SV is mixed with 0.5 mL of Sterile Water for Injection and used immediately,[3] while Egrifta WR is mixed with 1.3 mL of Bacteriostatic Water for Injection and discarded 7 days later.[4] Bacteriostatic water's own label says it is only for dissolving drugs as their manufacturer directs.[2] The bac water for peptides page covers that label in full, and how to store peptides covers what happens after mixing.
Mistakes the arithmetic cannot fix
Four mistakes give a wrong answer however good the calculator is.
- Unknown volume. If you are not sure how much liquid went in, the concentration is unknown, and so is every reading after it.
- mcg typed as mg. 250 mcg is 0.25 mg. The calculator has a unit switch; check it.
- Wrong syringe type. All unit numbers here are for U-100 syringes. See "U-100 syringe" in the glossary.
- A label that is wrong. The math assumes the vial holds what it says. Products sold as "research use only" are not checked by the FDA, so that assumption may not hold. See the safety page.
Related tools
- Units chartsPre-computed readings for 2, 5 and 10 mg vials
- mg ↔ mcg chartConversions and mcg per unit at each concentration
- Open formulasThe code behind every number, with tests
Frequently asked questions
Does adding more water weaken the peptide?
No. The vial holds the same number of milligrams whatever volume you add. More liquid only spreads them out, so the same amount takes more units on the syringe.
How much liquid for a 5 mg peptide vial?
The arithmetic gives options, not an answer. With 1 mL the vial is 5 mg/mL and each unit holds 50 mcg; with 2 mL it is 2.5 mg/mL and each unit holds 25 mcg; with 2.5 mL each unit holds 20 mcg. Which diluent is appropriate, if any, is a question for a pharmacist.
How do I find the concentration after reconstitution?
Divide the milligrams on the vial label by the millilitres of liquid you added. 10 mg in 2 mL is 5 mg/mL. Multiply by 10 to get micrograms per unit on a U-100 syringe: 50 mcg per unit.
Can I use the calculator for a vial that is already a liquid?
Yes, if you know the concentration. Enter any mg and mL that give the same mg/mL. A solution labeled 2 mg/mL can be entered as 2 mg in 1 mL.