Calculator methodology

The calculator requires these positive decimal values:

• the amount in the vial, in milligrams
• the liquid added, in millilitres
• a target amount supplied by the user, in milligrams or micrograms
• a U-100 syringe capacity of 30, 50, or 100 units

For U-100 syringes, 100 units equal 1 mL. One unit therefore equals 0.01 mL. Syringe units are volume markings, not milligrams or micrograms.

If the target amount is entered in micrograms, PepKit first converts it to milligrams.

target mg = target mcg ÷ 1,000

concentration (mg/mL) = vial amount (mg) ÷ liquid volume (mL)

draw volume (mL) = target amount (mg) ÷ concentration (mg/mL)

U-100 draw units = draw volume (mL) × 100

micrograms per U-100 unit = concentration (mg/mL) × 10

whole target amounts per vial = floor(vial amount ÷ target amount)

Suppose the vial amount is 5 mg, the liquid volume is 2 mL, and the user enters a target amount of 250 mcg.

1. 250 mcg ÷ 1,000 = 0.25 mg.
2. 5 mg ÷ 2 mL = 2.5 mg/mL.
3. 0.25 mg ÷ 2.5 mg/mL = 0.1 mL.
4. 0.1 mL × 100 = 10 U-100 units.

The result is 0.10 mL, which corresponds to 10 units on a U-100 syringe.

• Concentration is displayed to two decimal places.
• Micrograms per U-100 unit is displayed to one decimal place.
• Draw volume is displayed to two decimal places.
• Draw units are displayed as a whole number when the raw value is within 0.05 units of that number. Other values are displayed to one decimal place.
• Whole target amounts per vial are rounded down.
• Syringe fill percentage is displayed as a whole percent.

Calculations use the unrounded values. Display rounding does not feed back into later steps.

• PepKit flags a result that exceeds the selected syringe capacity.
• PepKit flags a draw below 2 units as difficult to measure.
• PepKit notes when a draw does not align with the assumed minor graduations: 1 unit for 30- and 50-unit syringes, and 2 units for 100-unit syringes.

Those checks describe the arithmetic and selected scale. They do not confirm the accuracy of a physical syringe or the suitability of a target amount.

Automated tests cover unit conversion, milligram and microgram inputs, whole and fractional syringe-unit results, invalid inputs, and syringe-capacity warnings. Each software release still requires a passing test run before deployment.

The current method was published on September 3, 2026. Material changes to formulas, units, or rounding rules will be recorded here with their effective date.