The 'liter' is a unit of volume in the system that is customary in 90 percent of the countries in the world,namely the metric system.
liter(metric) gallon(customary)
It is a customary unit.
The opposing systems are imperial and metric, not customary. But, meters are metric.
It is customary.
It is customary.
customary
It is customary.
The pound is NOT a metric unit.
Metric.
Metric
Metric