It's both.
Metric.
It is a customary unit.
The customary unit of capacity for a bathtub is gallons.
Capacity isn't a unit at all. It's a characteristic, or a property of an item, which can be measured in whatever suitable unit. Capacity of batteries is measured in amp hours. Capacity of a gas tank can come in either liters or gallons.
Turkey uses the Metric System.The only country that does not use the Metric System is the USA.
It is a customary unit.
The opposing systems are imperial and metric, not customary. But, meters are metric.
The pound is NOT a metric unit.
It is customary.
It can be more or less. An once (customary) is bigger than a gram (metric) but a pound (customary) is smaller than a kilogram (metric).
No a quart is a customary measurement for the capacity of liquid as where a Kilometer is a metric measurement for length
Metric.
Metric
Metric.
It is a customary unit.
customary
A "gran" is a German measurement, it is neither customary or metric. A "gram" is a metric unit.