Allowing the selection of measurement system

Most countries use the metric rather than the imperial system of measurement. Some industries, such as publishing, have invented and continue to use their own measurement systems. Transformation between measurement systems means not only reordering and changing delimiters and unit names or symbols, but also recalculating the numeric values.


Measurements must be presented in units that are familiar to the user. In publications that may be read by users worldwide, provide the metric dimensions first and then include culture-specific standards such as the imperial equivalents when necessary. When your product is designed for a particular industry, however, it may be more usable if you first show measurements in units usually employed by the industry.


Guideline C9

Allow the user to select the measurement system.

Example: A length of 1,000 inches in the USA transforms into 2 540 centimeters in France.


Example: Your product permits the user to design fonts used for publishing. The common unit of measure for font size is points, each of which is approximately 1/72 of an inch.

Many countries have more than one measurement system in daily usage.


Example: In the United Kingdom, weights are shown in kilograms, but road signs continue to show distances in miles.


Example: Canada is officially metric, but imperial measures continue to be used in such industries as the lumber industry.