SUMMARY
The term '1-inch sensor' in photography is a historical misnomer, originating from the outer diameter of glass vacuum tubes used in early television cameras. The active imaging area of these sensors, such as those in Sony RX100 cameras, measures approximately 13.2 x 8.8 mm with a diagonal of about 15.86 mm, significantly less than a true inch (25.4 mm). This naming convention persisted as solid-state sensors replaced tubes, allowing for easier integration into existing designs. The '1-inch type' designation is a category label, not a direct measurement, and is kept for commercial reasons as a larger-sounding descriptor.
TAKEAWAYS
The '1-inch' sensor name refers to the historical outer diameter of vacuum tubes, not the actual sensor dimensions.
A typical 1-inch type sensor has an active imaging area diagonal of approximately 16 mm.
This naming convention was retained when solid-state sensors replaced vacuum tubes in cameras.
The actual sensor size is about two-thirds of the nominal tube diameter, a legacy from old imaging technology.