Peptide Reconstitution Math, Step by Step

Calculators and charts are convenient, but the researchers who make the fewest mistakes are the ones who can do the reconstitution math by hand. It is not hard: the entire process is one formula and careful attention to units. This walkthrough takes it one step at a time so that, by the end, you can compute a concentration, reverse the calculation to check it, and catch the error that trips up almost everyone. Nothing here requires more than arithmetic you already know.

Step 1: Know the formula

There is exactly one relationship to remember:

Concentration = mass ÷ volume

Mass is how much peptide is in the vial. Volume is how much solvent you add. Concentration is how strong the finished solution is. Every other version of the calculation is this formula rearranged.

Step 2: Rearrange to solve for what you need

Depending on what you already know, you will want one of three forms:

• Solving for concentration: C = mass ÷ volume
• Solving for volume: volume = mass ÷ C
• Solving for mass: mass = C × volume

If you can rearrange one simple equation three ways, you can handle any reconstitution problem that exists.

Step 3: Get your units straight first

This is the step that actually causes errors. Decide up front whether you are working in milligrams or micrograms, and stick with it. The key conversion is:

1 mg = 1000 mcg

If a value is given in mg and another in mcg, convert one before you do anything else. An answer that is exactly 1000 times too big or too small is the signature of a unit slip, not a math error.

Step 4: A worked example, start to finish

Say a vial holds 10 mg of peptide and you want to add 2 mL of solvent. What is the concentration?

• Formula: C = mass ÷ volume
• Plug in: C = 10 mg ÷ 2 mL
• Result: 5 mg per mL

Now the reverse problem. You have a 5 mg vial and you want a final concentration of 2 mg per mL. How much solvent?

• Formula: volume = mass ÷ C
• Plug in: volume = 5 mg ÷ 2 mg per mL
• Result: 2.5 mL

Step 5: Always check by reversing

The fastest way to catch a mistake is to run the calculation backwards. If you added 2.5 mL to a 5 mg vial expecting 2 mg per mL, multiply concentration by volume: 2 × 2.5 = 5 mg. That matches the vial, so the math holds. Any time the reverse check does not return the original mass, something is wrong, usually a unit.

Quick reference

The number that has to be right

All of this arithmetic assumes the mass in the vial is exactly what the label says. If the vial contains less peptide than stated, every calculation you run will be confidently wrong. That is why a certificate of analysis is not a formality: it confirms the identity and amount of peptide, which is the one input your math cannot verify on its own.

Buying peptides with reliable labels in Canada

LYFE Science is a Canadian supplier and confirms every lot by HPLC and mass spectrometry, with a certificate of analysis available, so the mass you calculate with is the mass you actually received. We ship across Canada by Canada Post at a flat $25, free over $150, with same-day dispatch on orders paid before noon Eastern. We accept Interac e-Transfer and crypto (BTC, ETH, SOL, USDC, USDT), and packaging is plain and neutral.

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