Precision and sensible rounding
The definitions are exact, but a screen or worksheet cannot show every repeating quotient. Keep the source factor during calculation. Round the final result based on the measuring tool: a marked kitchen jug rarely justifies six decimal places.
Example: 3 US cups to milliliters
Multiply 3 × 236.5882365 to get 709.7647095 mL. A recipe may reasonably round that to 710 mL.
Try a custom amount: use the liquid volume converter when your value is not in the table.