Characteristic Impedance of Vacuum

The impedance free space offers to an electromagnetic wave: about 377 ohms.

Specifications & Metrics

symbol

Z0

status

Measured — CODATA 2022 adjustment

value

376.730313412 ± 5.9 × 10⁻⁸ ohm

Relative Scale in Constants

Core Principles & Analysis

• Equal to the square root of μ0/ε0, a pure consequence of Maxwell's equations.
• Antenna design starts here: match to 377 ohms or reflect.
• Defined exactly in the pre-2019 SI, now a measured consequence of α and Z0's definition.