# Reconstitution Maths: Three Formulas Behind Every Peptide Calculator > Concentration, draw volume, syringe units. Check any calculator by hand in a minute and see exactly where thousandfold errors creep in. Web page: https://peptidemedixeu.com/en/learn/peptide-reconstitution-calculator-explained/ · Peptide Medix EU · 3 min read · Updated: 2026-06-30 Three short formulas drive every peptide reconstitution calculator, and any output can be verified by hand inside a minute. The first: concentration equals peptide mass divided by diluent volume. The second: the volume to draw equals the amount you want divided by the concentration. The third: units on a U-100 [insulin syringe](https://peptidemedixeu.com/en/learn/insulin-syringes-for-research/) equal mL multiplied by 100. This guide takes each one through real laboratory numbers, identifies where the familiar tenfold and thousandfold mistakes originate, and shows what our reconstitution calculator does behind its interface. All of it is solution arithmetic for research material: it describes what sits in a syringe barrel, not what to do with it. ## The units involved - mg (milligram), the unit on the vial label: a BPC-157 vial contains 5, 10, 15 or 20 mg of powder. - mcg (microgram, µg), the unit working amounts are normally quoted in, with 1 mg equal to 1,000 mcg. This conversion causes more errors than any other; see micrograms vs milligrams. - mL (millilitre), the unit for diluent and for draws. - Units, the graduations on an insulin syringe. On the U-100 scale 100 units fill 1 mL, putting one unit at 0.01 mL. Units register volume alone and reveal nothing about peptide quantity until the concentration is known. ## Formula one: concentration Concentration in mg/mL equals vial mass in mg divided by [diluent volume](https://peptidemedixeu.com/en/learn/bacteriostatic-water-vs-sterile-water/) in mL. Take a 5 mg vial and add 2 mL of bacteriostatic water: 5 ÷ 2 gives 2.5 mg/mL, and multiplying by 1,000 gives 2,500 [mcg](https://peptidemedixeu.com/en/glossary/micrograms-vs-milligrams/)/mL. The physical steps of swabbing, running diluent down the glass and swirling appear in the peptide reconstitution guide, since this page deals purely with numbers. ## Formula two: volume for an amount Volume in mL equals the amount wanted in mcg divided by the concentration in mcg/mL. If an experiment needs 250 mcg from the 2,500 mcg/mL stock above, 250 ÷ 2,500 comes to 0.1 mL. Drawn from a denser 5,000 mcg/mL stock, that same 250 mcg occupies just 0.05 mL. Identical quantity, half the volume, which is why a syringe reading is meaningless unless the concentration is written on the vial label. ## Formula three: millilitres to units Units equal mL times 100 on a U-100 syringe, so 0.1 mL is 10 units and 0.05 mL is 5 units. Folding all three formulas together gives one expression: Units to draw = amount wanted (mcg) ÷ [vial mass (mg) × 1,000 ÷ diluent volume (mL)] × 100. That expression is the whole calculator. Worked through: a 10 mg vial, 3 mL of diluent, 300 mcg required. Concentration is 10 × 1,000 ÷ 3 = 3,333 mcg/mL. Volume is 300 ÷ 3,333 = 0.09 mL. Units: 9. ## Micrograms per unit at typical concentrations Scan the table along the rows before reconstituting. Should your protocol's amounts land at 1-2 units, the stock is too concentrated to measure reliably; should they run past the end of the barrel, it is too dilute. Keeping draws roughly between 5 and 40 units holds percentage error low on a 1 mL 31G insulin syringe, while the 0.5 mL 29G half-barrel spreads the same volumes across wider graduations for easier reading. Hardware selection is a subject in itself — see choosing [syringes and needles](https://peptidemedixeu.com/en/collections/syringes-vials/) for peptide research. ## Three recurring mistakes 1. The factor-of-1,000 slip: reading 0.25 mg as 25 mcg, or as 2,500 mcg. Write concentrations on the vial label in both mg/mL and mcg/mL so the conversion happens once at the bench and never again in your head. 2. The factor-of-10 slip: mixing up units with millilitres, or reading a U-100 barrel as though 10 units were 1 mL. Ten units is 0.1 mL. 3. The wrong-denominator slip: dividing by vial mass instead of concentration, which leaves the answer unaffected by how much diluent went in. If imagining twice the diluent does not change the result, the formula was misapplied. ## Where mass units fall short: molarity and IU Comparisons across peptides are normally made at matched molarity rather than matched mass, because molecular weights vary so widely: semaglutide is 4113.58 g/mol against 889.02 g/mol for TB-500, so 1 [mg of TB-500](https://peptidemedixeu.com/en/products/tb-500/) holds roughly 4.6 times more molecules than 1 mg of semaglutide. Converting mg/mL into molar concentration is dealt with in molecular weight, [moles](https://peptidemedixeu.com/en/learn/peptide-molecular-weight-and-moles/) and molarity. Some biologicals are labelled in international units, a measure defined by bioassay that has no universal conversion to mass; where a relationship exists for a given material, its certificate states it. ## Cross-checking yourself A useful habit is to calculate twice, once through the calculator and once by hand using the single-line formula, accepting the figure only when both agree. Then write vial mass, diluent, concentration and date onto the label and into a log sheet. In practice the usual failures are not arithmetic at all but unlabelled vials and diluent volumes changed midway through a study, both discussed in 10 common reconstitution and storage mistakes. For conversions outside this workflow, the unit converter and [molarity calculator](https://peptidemedixeu.com/en/glossary/molarity/) handle mass, volume and molar forms. ## Frequently asked questions ### How many micrograms does one syringe unit hold? That depends entirely on the solution's concentration, because one unit on a U-100 syringe is simply 0.01 mL of volume. At 2.5 mg/mL (2,500 mcg/mL) a unit carries 25 mcg, at 5 mg/mL it carries 50 mcg, and at 10 mg/mL it carries 100 mcg. Since a unit measures volume, the same reading holds different quantities from different stocks. ### Which formula does a reconstitution calculator use? Three steps in sequence: concentration in mcg/mL equals vial mass in mg times 1,000 divided by diluent volume in mL; volume in mL equals the amount wanted in mcg divided by that concentration; units equal volume times 100. In one line, units = amount ÷ (mg × 1,000 ÷ mL) × 100. A calculator disagreeing with that hand calculation is being given wrong inputs. ### Does 1 mg equal 1,000 mcg? It does, exactly, just as 1 gram equals 1,000 milligrams. The mg-to-mcg step is where thousandfold errors most often enter reconstitution arithmetic, which is why labels should carry the concentration in both forms, such as "2.5 mg/mL = 2,500 mcg/mL", written at the moment of reconstitution. ### Do units convert to millilitres identically on all syringes? Only within one scale. On the standard U-100 scale, 100 units fill 1 mL whatever the barrel size, be it 0.3, 0.5 or 1 mL. U-40 syringes also exist, holding 40 units per mL, and their graduations cannot be used with U-100 arithmetic. Everything stocked here is U-100, so check the scale printed on any barrel obtained elsewhere. ### Why convert mg/mL into molarity? Because identical masses of different peptides contain very different molecule counts. Dividing concentration in g/L by molecular weight in g/mol yields molarity: 1 mg/mL of semaglutide (MW 4113.58) is about 243 µM, while 1 mg/mL of TB-500 (MW 889.02) is about 1,125 µM. Receptor and cell-based comparisons only mean anything at matched molar concentration. ### What concentration should I aim for? Whichever puts your routine draws in the legible middle of the syringe, around 5 to 40 units on a U-100 barrel. Work backwards from the amounts your protocol needs, divide them by candidate concentrations, and choose the diluent volume that lands those draws inside that range without exceeding the vial's capacity, typically about 2 to 2.5 mL in a standard 3 mL research vial. --- For laboratory research use only. This page is provided for scientific and educational information. Materials referenced here are sold strictly for in-vitro laboratory research by qualified professionals — not for human or veterinary use, and nothing on this page is medical advice.