dimensionless quantity

Dimensionless quantities, or quantities of dimension one, are quantities defined in a manner that prevents their aggregation into units of measurement. Typically expressed as ratios that align with another system, these quantities do not necessitate explicitly defined units. For instance, alcohol by volume (ABV) represents a volumetric ratio; its value remains independent of the specific units of volume used, such as in milliliters per milliliter (mL/mL). A characteristic number is a quantity of dimension one defined by a combination of quantities possibly involving multiplication and exponentiation, not just a division.

The number one is recognized as a dimensionless base quantity. Radians serve as dimensionless units for angular measurements, derived from the universal ratio of 2π times the radius of a circle being equal to its circumference.