Peptide calculator: reconstitution and half-life

Q: How much bacteriostatic water is needed for a 10mg bottle?

This depends on the desired concentration: 1 ml yields 10 mg/ml, 2 ml yields 5 mg/ml, and 3 ml yields approximately 3.3 mg/ml. A 3 ml bottle of bacteriostatic water is generally sufficient to reconstitute one bottle.

Two free laboratory tools, requiring no registration: the reconstitution calculator provides the concentration of a lyophilized peptide based on the vial quantity and the volume of water added, and the half-life calculator shows the remaining peptide concentration over time. These calculations do not constitute a dosage recommendation.

Bacteriostatic water 3 ml – €5 Reconstitution Pack – €14.90

Reconstitution calculator

Choose a bottle or enter its quantity, then the volume of bacteriostatic water added: the concentration is displayed immediately.

Bottle Peptide in the vial (mg) Added bacteriostatic water (ml)

Concentration–mg/ml

That is, in micrograms–µg/ml

Peptide in 0.1 ml (10 U-100 graduations)– µg

Peptide in 0.01 ml (1 U-100 graduation)– µg

Inverse calculation: what volume of water is needed for a given concentration?

Target concentration (mg/ml)

Add water– ml

How is the concentration calculated?

The formula is simple:concentration (mg/ml) = amount of peptide (mg) ÷ volume of water (ml)Water does not change the amount of peptide in the bottle; it only determines its dilution. Multiply by 1000 to convert to micrograms per milliliter.

Bottle	Water added	Concentration	In 0.1 ml
Retatrutide 10 mg	1 ml	10 mg/ml	1000 µg
Retatrutide 10 mg	2 ml	5 mg/ml	500 µg
Retatrutide 20 mg	2 ml	10 mg/ml	1000 µg
Cagrilintide 5 mg	2 ml	2.5 mg/ml	250 µg
GHK-Cu 50 mg	3 ml	16.7 mg/ml	1667 µg

Choosing the volume is a compromise: less water results in a more concentrated solution, while more water makes volumes easier to measure. Best practices for reconstitution (wall of the bottle, no shaking, refrigerated storage) are detailed in our guide to bacteriostatic water.

Read a U-100 syringe

A graduated syringe labeled "U-100" counts100 graduations per 1 mlOne graduation equals 0.01 ml and ten graduations equal 0.1 ml. The 0.3 ml, 0.5 ml, and 1 ml syringes have 30, 50, and 100 graduations, respectively. The calculator above converts the concentration into the amount of peptide per graduation, which is useful for laboratory sampling.

Half-life calculator

The half-life is the time it takes for half of a peptide to be eliminated. Choose a peptide (or enter a half-life) and a number of days:

Peptide Half-life (days) Days elapsed

Remaining portion– %

Eliminated portion– %

Near-complete elimination (5 half-lives, 97%)–days

Remaining portion of a single quantity, week by week

Week 1–

Week 2–

Week 3–

Week 4–

Week 5–

The calculation assumes regular elimination (first-order kinetics): remaining portion = 100% × 0.5^{days ÷ half-life}It describes a single quantity and does not take absorption into account.

Half-life of the main peptides studied

Peptide	Half-life	What extends it	Source
Retatrutide	approximately 6 days	fatty acid chain (linked to albumin)	Coskun et al., Cell Metabolism 2022
Tirzepatide	about 5 days	fatty acid chain	FDA notice (Mounjaro)
Semaglutide	approximately 7 days	fatty acid chain	EMA (Ozempic) instructions
Cagrilintide	approximately 7 days	fatty acid chain	Phase 1 studies (Novo Nordisk)
Tesamorelin	less than an hour	—	FDA notice (Egrifta)

Calculate using the actual quantity in the bottle

A vial labeled 10 mg does not always contain exactly 10 mg. The Certificate of Analysis (COA) indicates the measured quantity: in our Janoshik-tested retatrutide lots, over 11.4 mg per 10 mg vial and over 22.7 mg per 20 mg vial. For an exact concentration, enter this measured quantity into the calculator. All reports are available on the retatrutide COA page.

Reconstitution supplies and prices

Product	Content	Price
Bacteriostatic water 3 ml	1 bottle, benzyl alcohol 0.9%	5,00 €
Reconstitution Pack	Bacteriostatic water 3 ml, syringes, gloves, swabs (peptide-free)	14,90 €
R10 Pack	Retatrutide 10 mg + reconstitution kit	69,90 €
R20 Pack	Retatrutide 20 mg + reconstitution kit	109,90 €

Retatrutide with its reconstruction kit
Lyophilized vial, blind-tested by Janoshik, with bacteriostatic water, syringes, and swabs. Shipping €10, dispatched from the European Union.
R10 Pack – €69.90 Retatrutide R3 10 mg – €59.90

Frequently Asked Questions

How to calculate the concentration of a reconstituted peptide?

The amount of peptide in the vial (in mg) is divided by the volume of water added (in ml). A 10 mg vial reconstituted with 2 ml gives 5 mg/ml, or 5,000 µg/ml.

How much bacteriostatic water is needed for a 10mg bottle?

This depends on the desired concentration: 1 ml gives 10 mg/ml, 2 ml gives 5 mg/ml, and 3 ml gives approximately 3.3 mg/ml. A 3 ml bottle of bacteriostatic water is generally sufficient to reconstitute one bottle.

How many graduations are there in 1 ml on a U-100 syringe?

100 graduations: one graduation equals 0.01 ml and ten graduations equal 0.1 ml. A 0.5 ml syringe therefore has 50 graduations.

What is the half-life of retatrutide?

Approximately 6 days according to phase 1 studies (Coskun et al., 2022), thanks to a fatty acid chain that binds it to albumin. This explains the weekly rhythm of clinical trials.

Does the calculator indicate a dose?

No. It converts a quantity and a volume into a concentration, and calculates a theoretical decay. It does not recommend any quantity to administer: MyPeptide products are intended for laboratory research.

Sources: Coskun T. et al., Cell Metabolism 2022 (retatrutide, phase 1); FDA and EMA product information leaflets (tirzepatide, semaglutide, tesamorelin). MyPeptide products are intended for scientific laboratory research use only.