Peptide reconstitution calculator

How does peptide reconstitution work?

A lyophilised peptide arrives as a dried powder. Reconstitution is adding a liquid — usually bacteriostatic water — so the compound is in solution and can be measured by volume rather than by mass.

The mass in the vial does not change. What the liquid determines is the concentration, and therefore how much volume carries any given amount.

The arithmetic, step by step

1. 01Convert the vial to micrograms. Multiply the milligrams on the vial by 1,000.
2. 02Divide by the diluent volume. That gives the concentration in mcg per mL.
3. 03Divide your amount by the concentration. That gives the volume in mL.
4. 04Multiply the volume by 100. On a U-100 syringe, 1 mL is 100 units, so that is the marking.

mg × 1000 ÷ mL = mcg/mL
mcg ÷ (mcg/mL) = mL · mL × 100 = units

How to read a U-100 syringe

A U-100 insulin syringe is marked in units where 100 units is exactly 1 mL. One unit is 0.01 mL. The markings measure volume and nothing else — they say nothing about what is dissolved in it.

U-100 versus U-40 syringes

A U-40 syringe holds 40 units per mL. The same numeral therefore draws two and a half times the volume it would on a U-100. Every figure this page produces assumes U-100; if a syringe is marked U-40, the units output does not apply to it.

Common conversion errors

Reading a U-40 syringe as U-100

A U-40 syringe holds 40 units per mL, not 100. The same marking draws two and a half times the volume. This is the single most common way a measurement ends up wrong by a large factor.

Confusing mg and mcg

1 mg is 1,000 mcg. Slipping a decimal here is a thousand-fold error, and the numbers involved are small enough that it does not look obviously wrong.

Assuming more diluent means less compound

It does not. The vial holds the same amount of peptide however much water is added — the concentration changes, so the volume you draw changes with it.

Treating syringe units as lab units

The "units" on a syringe are a volume marking. The "units" on some product labels are a measure of biological activity. They are unrelated.

What this calculator does not do

• It does not suggest an amount to measure. The third field is yours to fill; nothing on this site will put a number in it.
• It does not know what is in your vial. The arithmetic assumes the label is accurate, which is a separate question — see the vendor records.
• It does not account for loss in the syringe, the needle or the vial stopper.

Common questions about peptide calculations