Full-well Capacity
The maximum number of electrons a photosite can hold before it saturates and stops responding to further light.
Measured in
e⁻ (electrons)
In depth
Full-well capacity sets the top of the dynamic range: once reached, additional photons contribute nothing and the highlight clips. Larger photosites hold more electrons, which is the real basis of the claim that bigger pixels have better dynamic range — though at the image level, more small pixels can compensate through averaging.
Examples in practice
A photosite with a 50,000-electron capacity clips as soon as that many are collected, no matter how much brighter the subject gets.