Reconstitution math step by step: work out concentration in mg/mL and convert a target dose to units on a U-100 syringe, with a worked example.
Key points
- 01The three numbers the math needs. To convert from a vial to a readable syringe mark, you need three figures: the amount of peptide in the vial (in milligrams), the volume of diluent you add (in millilitres), and the target dose (usually in micrograms). This page describes the calculation method in a research context and is not medical advice or a dosing recommendation.
- 02Step 1: find the concentration (mg per mL). Divide the peptide amount by the diluent volume. Example: a 5 mg peptide vial plus 2 mL of bacteriostatic water gives 5 divided by 2, which is 2.5 mg/mL. The diluent volume is a choice that sets the concentration; more diluent means a lower concentration and more units per dose.
- 03Step 2: convert mg to micrograms. Because doses are usually stated in micrograms, convert: 1 mg equals 1000 mcg. So 2.5 mg/mL becomes 2500 mcg/mL. This step heads off the most common error, mixing up milligrams and micrograms by a factor of a thousand.
- 04Step 3: translate to the U-100 syringe. A U-100 insulin syringe holds 100 units per 1 mL, so one unit equals 0.01 mL. At 2500 mcg/mL, 1 mL contains 2500 mcg, so 1 unit equals 25 mcg. The post on insulin syringe units and sizes explains the markings, and the peptide calculator does the arithmetic for you.
- 05Full example: 5 mg vial, 2 mL, target 250 mcg. Concentration is 2500 mcg/mL, and one unit equals 25 mcg. For a 250 mcg target, divide 250 by 25 to get 10 units. For 500 mcg it would be 20 units. The target dose itself is not a recommendation from this page; it is the number from the protocol you are following.
- 06Read units on the syringe, not millilitres. Draw to the calculated mark in units, not millilitres, because the U-100 syringe is scaled in units. Ten units is one tenth of a millilitre. The guide on drawing up medication covers pulling to the right mark without bubbles.
- 07Common arithmetic slips. The recurring errors are mixing up milligrams and micrograms by a factor of a thousand, recording the diluent volume wrong, treating units as millilitres, or assuming a different vial size than you actually have. Check each of the three starting numbers before you divide.
- 08Cross-check and label the vial. Cross-check the result with the peptide calculator, and label the vial with the concentration and reconstitution date. The post on how to reconstitute peptides covers the technique, and the comparison of bacteriostatic and sterile water explains why the diluent you choose changes the usable window.
Frequently asked questions
How do I calculate a peptide dose in units?+
In three steps: concentration equals peptide amount divided by diluent volume (5 mg in 2 mL gives 2.5 mg/mL); convert to micrograms (2.5 mg/mL equals 2500 mcg/mL); then divide by the units on a U-100 syringe (1 mL equals 100 units, so 1 unit equals 25 mcg). A 250 mcg target is then 10 units.
How much bacteriostatic water should I add?+
The diluent volume is a choice that sets the concentration, not a fixed rule. More water gives a lower concentration and more units per dose, which can make small doses easier to read. Common values are 1 to 3 mL per vial. Run the math with the volume you choose, as shown in the example.
What does one unit on an insulin syringe equal in micrograms?+
It depends on the concentration. On a U-100 syringe, 1 mL holds 100 units. At 2500 mcg/mL, one unit equals 25 mcg; at a different concentration the value differs. Always work it out for your specific vial rather than reusing a number from another preparation.
Why work in micrograms instead of millilitres?+
Because protocols state doses in micrograms, but the syringe is scaled in units. The intermediate step through concentration in mcg/mL connects the two. Mixing up milligrams and micrograms by a factor of a thousand is the most consequential arithmetic error.
Can I let the calculator do the math?+
Yes, the peptide calculator handles the arithmetic once you enter the vial amount, diluent volume, and target dose. It is still worth understanding the method so you can check the three starting numbers and recognize an implausible result.