centiamp

A centiamp (cA) is a unit of electric current equal to 0.01 amperes, or 10 milliamps. It sits in the metric hierarchy between the ampere and the milliamp, but you will rarely encounter it in modern practice. The SI prefix centi- means one hundredth, so the math is straightforward; the awkwardness lies in its collision with more useful units at nearby scales.

The unit appeared in early metric standardization but found little foothold in electrical work. Milliamps and microamps dominate measurement ranges where current is small; full amperes or tens of amperes cover everything larger. A centiamp occupies an uncomfortable middle ground: large enough that you would more naturally state it as 0.01 A or 10 mA, small enough that it rarely corresponds to actual component ratings or equipment specifications. This is why metrology texts list it formally but field technicians almost never use the term.

You may still see centiamp notation in very old European technical documents, older textbooks, or historical circuit specifications, particularly from mid-twentieth century sources. In such contexts, a device drawing 50 cA would be more commonly written today as 0.5 A or 500 mA depending on the precision required and the audience. Modern standards and practice have consolidated around milliamps for small currents and full amperes for larger ones, leaving centiamp as a ghost unit in official SI tables.

In calibration and inspection work, metrologists recognize centiamp as a valid SI multiple but rarely use it in actual uncertainty budgets, tolerance statements, or equipment specifications. Analog meters built before the 1980s sometimes carried centiamp markings on their scales, but digital instruments measure and display in units more intuitive to the task at hand. If you encounter a centiamp specification in legacy equipment documentation, translating it to milliamps or amperes as context demands will always clarify the intent.