How to reconstitute peptides: the math, step by step

How to reconstitute peptides: the five numbers

Reconstituting a peptide comes down to five numbers, worked out in this order:

1. Vial amount. The mg printed on the label, for example 5 mg.
2. Diluent. The liquid the product's label names. Approved products specify it; the two current tesamorelin products use different ones.^[3][4]
3. Volume. How much liquid goes in, for example 2 mL. For an approved product the label sets this too.
4. Concentration. Vial mg ÷ mL: 5 ÷ 2 = 2.5 mg/mL, which is 25 mcg in each U-100 unit.
5. Units for an amount. Amount ÷ concentration × 100: 250 mcg is 0.25 ÷ 2.5 × 100 = 10 units.

The reconstitution calculator runs steps 4 and 5 for any numbers, and the bac water page covers step 2 in detail.

How to mix peptides: what approved labels say

The only authoritative mixing instructions are those on approved labels, and they differ by product.

For peptides with no approved label, nobody has published tested instructions for diluent, mixing or stability. Bacteriostatic water's own label says it is only for dissolving drugs "according to instructions of the manufacturer of the drug".^[6]

Peptide vial sizes on approved labels

Approved peptide products come in fixed vial sizes chosen with a fixed volume of liquid, so the concentration is known before anyone does any math.

Products sold as "research use only" come in whatever sizes the seller chooses, with no labeled liquid volume. The chart below covers the common round sizes, and the peptide dosage calculator handles any size.

Peptide reconstitution chart

This chart gives the concentration and the micrograms in 10 units for common vial sizes and liquid volumes.

The four formulas

Every number on this site comes from four lines of arithmetic. Two facts make them work: one milligram is 1,000 micrograms,^[2] and a U-100 insulin syringe holds 100 units per millilitre.^[1]

Two more lines are the same algebra solved for a different unknown. One gives the amount in a syringe reading, the other the liquid needed for a chosen reading:

How to calculate peptide dosage: worked examples

Forward. 5 mg vial, 2 mL of liquid, 250 mcg wanted. C = 5 ÷ 2 = 2.5 mg/mL. V = 0.25 ÷ 2.5 = 0.1 mL. Units = 0.1 × 100 = 10 units. The vial covers 5 ÷ 0.25 = 20 such amounts.

Reverse. Same vial, 10 units drawn. 10 ÷ 100 × 2.5 = 0.25 mg (250 mcg).

Backwards for the liquid. To make 250 mcg read as 10 units from a 5 mg vial: 10 × 5 ÷ (0.25 × 100) = 2 mL.

The code that runs the calculator

This is the source of the calculator's math, read from the code file when the site is built, so it always matches what your browser runs. It has no dependencies and makes no network requests.

export const UNITS_PER_ML = 100;
 
export const SYRINGES = [
  { id: '30', ml: 0.3, units: 30, label: '0.3 mL · 30 units' },
  { id: '50', ml: 0.5, units: 50, label: '0.5 mL · 50 units' },
  { id: '100', ml: 1, units: 100, label: '1 mL · 100 units' },
];

function positive(n) {
  return typeof n === 'number' && Number.isFinite(n) && n > 0;
}
export function nearestMark(units, syringeUnits) {
  const step = syringeUnits >= 100 ? 2 : 1;
  return Math.round(units / step) * step;
}

/**
 * Reconstitution: powder vial (mg) + diluent (mL) -> how far to draw for a dose.
 * @returns {{ok:true, concMgPerMl:number, mcgPerUnit:number, volumeMl:number, units:number,
 *   dosesPerVial:number, syringeUnits:number, fitsSyringe:boolean, tooSmall:boolean, markUnits:number}
 *   | {ok:false, error:string}}
 */
export function reconstitute({ vialMg, waterMl, doseMg, syringeUnits = 100 }) {
  if (!positive(vialMg)) return { ok: false, error: 'vial' };
  if (!positive(waterMl)) return { ok: false, error: 'water' };
  if (!positive(doseMg)) return { ok: false, error: 'dose' };
  if (doseMg > vialMg) return { ok: false, error: 'dose-exceeds-vial' };
  const concMgPerMl = vialMg / waterMl;
  const volumeMl = doseMg / concMgPerMl;
  const units = volumeMl * UNITS_PER_ML;
  return {
    ok: true,
    concMgPerMl,
    mcgPerUnit: (concMgPerMl * 1000) / UNITS_PER_ML,
    volumeMl,
    units,
    dosesPerVial: vialMg / doseMg,
    syringeUnits,
    fitsSyringe: units <= syringeUnits + 1e-9,
    tooSmall: units < 2,
    markUnits: nearestMark(units, syringeUnits),
    marks: markBracket(units, syringeUnits),
  };
}

/** Reverse: units drawn on a U-100 syringe -> mg delivered. */
export function unitsToMg({ vialMg, waterMl, units }) {
  if (!positive(vialMg)) return { ok: false, error: 'vial' };
  if (!positive(waterMl)) return { ok: false, error: 'water' };
  if (!positive(units)) return { ok: false, error: 'units' };
  const concMgPerMl = vialMg / waterMl;
  const volumeMl = units / UNITS_PER_ML;
  return { ok: true, concMgPerMl, volumeMl, mg: volumeMl * concMgPerMl };
}

/** How much diluent makes a dose land on a chosen number of units. */
export function waterForTargetUnits({ vialMg, doseMg, targetUnits }) {
  if (!positive(vialMg)) return { ok: false, error: 'vial' };
  if (!positive(doseMg)) return { ok: false, error: 'dose' };
  if (!positive(targetUnits)) return { ok: false, error: 'units' };
  return { ok: true, waterMl: (targetUnits * vialMg) / (doseMg * UNITS_PER_ML) };
}

Known answers it is tested against

An automated test suite checks the functions above before every deploy. The table is generated by those same functions when the page is built, so you can check each row with a pocket calculator.

Rounding and warnings

The calculator rounds only what it displays, and it warns about readings that are too small, too large or impossible.

• Display rounding. Units show one decimal place, mL three, mg/mL three. The math itself is not rounded.
• Nearest mark. When a result falls between marks, the calculator names the nearest one: 1-unit marks on 30- and 50-unit syringes, 2-unit marks on 100-unit syringes. Check your own syringe, because markings vary.
• Too small to measure. Readings under 2 units trigger a warning, because a misread of one line is then a large share of the amount.
• Too big for the syringe. Readings above the selected syringe's capacity are flagged.
• Impossible inputs. Zero, negative or missing numbers, and amounts larger than the whole vial, return an error message instead of a number.

What the formulas cannot know

The formulas cannot know whether a vial holds what its label says.

The calculator also cannot tell you whether an amount is safe or appropriate. It does not know what the substance is. See the safety page and the individual peptide pages for regulatory status and evidence.

Use the tools

• Peptide calculatorFormulas 1–4, live
• Units checkerThe reverse formula, live
• Reconstitution guideSolving for the liquid volume