Or, at least give the SI unit first, then a day-to-day formulation in parentheses.
The SI units are not just more useful for scientific minded readers, but also for international readers in general, who don't share the same cultural background and hence have no feeling for these "day-to-day formulations" anyway, because it isn't their day-to-day. For example, a German author might write:
| The area is as large as 7.2 km², which are 1000 football fields.
Without the SI unit (7.2 km²), this would be very confusing. Of course, the author meant association football (soccer) fields, not American football fields. But who in the international audience would have caught that, especially if I didn't state author's national background upfront? Even more importantly, which percentage of the international readership has developed a intuition about the size of a football field?
The SI units are not just more useful for scientific minded readers, but also for international readers in general, who don't share the same cultural background and hence have no feeling for these "day-to-day formulations" anyway, because it isn't their day-to-day. For example, a German author might write:
| The area is as large as 7.2 km², which are 1000 football fields.
Without the SI unit (7.2 km²), this would be very confusing. Of course, the author meant association football (soccer) fields, not American football fields. But who in the international audience would have caught that, especially if I didn't state author's national background upfront? Even more importantly, which percentage of the international readership has developed a intuition about the size of a football field?