U-100 is a scale, not a syringe capacity
U-100 indicates 100 scale units per mL. A 0.3 mL U-100 syringe holds 30 units, a 0.5 mL syringe holds 50, and a 1.0 mL syringe holds 100. They all use the same units-per-mL conversion.
1 U-100 unit = 0.01 mL
10 units = 0.1 mL
30 units = 0.3 mL
50 units = 0.5 mL
100 units = 1 mLA number of units does not identify a peptide mass
At 5 mg/mL, 0.02 mL contains 100 mcg. At 2.5 mg/mL, the same volume contains 50 mcg. Both volumes correspond to 2 U-100 units. Concentration is what connects mass with the volume marking.
Changing capacity changes the drawing, not the conversion
The same 0.02 mL result remains 2 U-100 units on each supported capacity. It occupies a different fraction of a 30-unit, 50-unit or 100-unit barrel. If a result exceeds the selected capacity, the calculator displays the mismatch instead of showing a misleading full scale.
U-100 syringe units are not biological IU
An international unit describes a defined biological activity for a specific substance. It is not a general mass or volume unit. You cannot convert the mg of an arbitrary peptide to IU using a universal ratio.
This calculator supports U-100 volume markings only. It does not convert biological IU, U-40 or U-500 devices, pen clicks or nasal spray actuations.
Graduations and displayed precision
The visible scale is illustrative. Actual syringe graduations vary, and mathematical precision does not guarantee that a device can resolve that volume. Results are not silently rounded to a nearby physical mark.
FDA has described errors arising from confusion between mass, volume and units. Keep source values and device markings explicit.