Calculation methodology

The three steps

1. Concentration — vial contents (mg) ÷ water added (mL) = mg per mL (shown with mcg equivalents).
2. Volume — your dose ÷ concentration = mL to draw.
3. Units — mL × 100 = marks on a U-100 insulin syringe (100 units per mL).

(dose in mcg ÷ concentration in mcg/mL) × 100 = U-100 syringe units

Supported units and assumptions

• Mass: milligrams (mg) and micrograms (mcg); 1 mg = 1,000 mcg
• Volume: millilitres (mL)
• Syringe scale: U-100 — 100 units per mL (1 unit = 0.01 mL), for 0.3 / 0.5 / 1.0 mL barrels

See mg vs mcg and how to read an insulin syringe.

Rounding and display

The shared engine rounds intermediate values for display (for example units to a practical number of decimals) using a stable roundTo helper. Visible working steps use locale-stable formatting. If a result falls between syringe tick marks, a warning may note the nearest whole unit — that is measurement feedback, not a dose recommendation.

Input validation

Non-positive or non-finite inputs are rejected. The engine may warn when a calculated draw exceeds a selected syringe capacity, when a dose exceeds the vial mass entered, or when a draw is extremely small. Warnings do not invent missing inputs or choose values for you.

Engine testing and parity

Web calculators call the shared @pepexact/engine package. Automated tests cover unit conversion, draw calculation, diluent calculation, and round-trip consistency so future clients (including a planned iOS app) can stay numerically aligned. Compound pages use the same calculator; only headings and educational context change.

Limitations

• Does not verify product identity, purity, or sterility
• Does not determine legality or regulatory approval
• Does not recommend peptides, amounts, water volumes, or protocols
• Assumes U-100 unless you convert for another scale yourself

Try the peptide calculator. Policy: editorial policy.