Understanding Sensor Sizes

In DSLRs, the senor size is always clearly mentioned in mm or as a standard type (APS-C or APS-H), which is easy to understand. However, in compact cameras, a sensor size is expressed in the form of inches (for instance, 1/2.3-inch or 1/1.7-inch). Can you please explain how this works and how I can compare the size of a compact camera’s sensor and a DSLR sensor?
Mehernosh Dhondy, via email

Sensor sizes of compact cameras and DSLRs are expressed using completely different methods. DSLR sensors are expressed in mm—for example, a full-frame camera has a sensor of size 36 X 24mm. Compact camera sensor measurement follow an older, non-standard system used with older video sensors and television tubes. This is because all compact camera sensors generally follow an aspect ratio of 4:3, which matches the ratios of most computer monitors, so that images can be viewed without cropping.

Unfortunately, it is not as simple to follow as DSLR sensor measurements. In effect,1/1.7-inch is about 7.6 X 5.7mm while 1/2.3-inch is approximately equal to 6.1 X 4.6mm, which several times smaller than the smallest DSLR sensor.