Reconstituting a lyophilized peptide is fundamentally a dilution problem: a known mass of peptide, dissolved into a chosen volume of solvent, gives a known concentration. The maths is simple once the relationship is clear — the part researchers usually want a tool for is avoiding an arithmetic slip when converting between mg, mL, and mcg per unit.
The core relationship
Concentration (mg/mL) is simply the total peptide mass in the vial divided by the volume of solvent used to reconstitute it. A 10mg vial reconstituted with 2mL of solvent, for example, produces a solution at 5mg/mL — the same 10mg of peptide is just distributed across 2mL rather than sitting as dry powder.
Everything else — volume per unit dose in an injection-style protocol, or total units drawn on a syringe scale — follows from that single concentration figure once it's calculated correctly.
Why more solvent isn't automatically better
Adding more solvent lowers concentration and increases the volume needed for a given amount of peptide, while less solvent raises concentration and reduces that volume. Neither direction is inherently correct — the right choice depends on what volume range is practical to measure accurately with the equipment on hand, which is a protocol design decision, not a fixed rule.
Cost-per-mg, separately
Cost-per-mg is a different calculation from concentration, and the two are easy to conflate. It's simply a variant's price divided by its total peptide mass, which makes it possible to compare value across differently sized variants of the same product on a like-for-like basis rather than comparing sticker prices alone.
Our concentration and cost-per-mg calculators handle both of these calculations directly — useful as a cross-check against your own working, not a replacement for it.