We often have to use measurements in Wikitravel -- for the distances between places, for the altitude of mountains, for the temperature of deserts, for the volume of a glass of beer. This style guideline gives some suggestions for how to specify and format measurements.
Use local units of measurement
When showing a measurement, use the local system of units for the destination you're describing. This is the system that travelers will see on road signs, local maps, menus, food packages, weather reports, etc.
For most of the world, this is the metric system. For the United States of America, it's the "imperial" system (miles, gallons, pounds). In some cases, the systems are mixed -- for example, in the United Kingdom, distance is measured by kilometers, but beer is served by the pint. We favor accuracy over consistency.
If the measurement spans multiple countries, use metric.
For articles that don't deal with a particular destination (like travel topics), use metric.
It's easier for travelers to visualize measurements if they're converted to their own country's units. For this reason, it's best to provide conversions for measurements into both metric and imperial, the two systems most widely used in the English-speaking world.
If the preferred units are metric, provide imperial measurements in parentheses after. If the preferred units are imperial, provide metric measurements in parentheses. If for some reason the local unit is neither metric nor imperial, provide first metric then imperial in parentheses afterwards.
Don't repeat conversions unnecessarily.
The following are some examples of good practice for measurements.