Electric current measures the rate of flow of electric charge through a conductor. The SI base unit is the ampere (A), defined since 2019 via the fixed elementary charge e = 1.602176634 × 10⁻¹⁹ C, making 1 A exactly 1/e elementary charges per second. Named after André-Marie Ampère, the ampere is one of the seven SI base units.
In practice, current values span many orders of magnitude. Integrated circuits operate at microamperes (µA) to milliamperes (mA); USB devices draw up to 3 A; household appliances use 1–15 A; electric vehicle motors can draw hundreds of amperes; and industrial arc furnaces operate at kiloamperes (kA). Milliamperes are the standard unit for electronics and sensor circuits; as little as 10 mA through the heart can be fatal.
| 1 A | = 1000 mA |
| 1 mA | = 1000 µA |
| 1 kA | = 1000 A |
| USB 2.0 max | 500 mA |
| USB-C PD | up to 5 A |
| Typical LED | 20 mA |