Peptide Calculator

When people prepare peptides, the most common mistake is mixing up three different numbers: vial mass, concentration, and delivered dose. The vial label tells you total peptide mass in milligrams. That mass is fixed. Once you add diluent, the math shifts to concentration per milliliter, and only then can you calculate how many units to draw. If you remember one equation, make it this one:

Peptides are polymers of amino-acid residues connected by amide bonds. In molecular-weight calculations, you usually sum residue masses and then account for terminal groups. A simple sequence estimate can be written as:

That molecular perspective matters because two peptides can both be labeled as "5 mg" while representing very different molar amounts. Five milligrams of a 1,000 Da peptide contains more molecules than five milligrams of a 3,000 Da peptide. If your protocol is molar (for example, nanomoles per kilogram), sequence mass is not optional - it is the core conversion.

Reconstitution itself is straightforward: add a known sterile diluent volume, dissolve gently, then compute concentration. For example, if you reconstitute 10 mg into 2.5 mL, concentration is 4 mg/mL. A 0.25 mg dose then needs 0.0625 mL, which equals 6.25 units on a U-100 syringe. The same dose from a 10 mg into 1.0 mL reconstitution would need only 2.5 units. Same peptide, same target dose, different draw volume. This is why documenting your exact dilution in a log is essential.

Amino-acid composition also affects behavior after administration. Hydrophobic and aromatic-rich peptides can interact differently with membranes than highly polar sequences, and that can influence absorption profiles. Post-translational modifications, cyclization, and salt forms can shift solubility and handling requirements as well. From a practical standpoint, if a solution is hard to dissolve or repeatedly precipitates, it is often a formulation issue rather than a dosing issue.

Bioavailability adds another layer. Oral peptide delivery is often limited by proteolytic degradation and poor intestinal permeability, so many protocols use subcutaneous or intramuscular routes to improve exposure. Even with injection, local tissue environment, injection depth, and timing consistency can affect observed response. That means dosing precision is necessary but not sufficient; administration consistency matters too. If outcomes vary unexpectedly, check handling, storage, and route consistency before assuming the concentration math is wrong.

Finally, treat concentration tools as safeguards, not shortcuts. Verify units every time (mg versus mcg, mL versus units), double-check decimal placement, and avoid "mental math" during rushed preparation. Good lab or clinical practice uses a repeatable checklist: confirm vial strength, confirm diluent volume, confirm target dose, compute draw volume, and document each step. Small arithmetic errors can lead to large relative dosing differences when volumes are tiny.