The precise size or diameter of a quark is not well-defined in the context of our current understanding of particle physics. Quarks are considered to be elementary particles, which means they are not made up of smaller constituents. As such, they are considered point-like particles without any internal structure or spatial extent.
The Planck length, on the other hand, is a theoretical concept derived from the fundamental constants of nature, including the speed of light, Planck's constant, and the gravitational constant. It represents the scale at which quantum gravitational effects are expected to become significant.
The Planck length is incredibly small, approximately 1.6 x 10^-35 meters. It is many orders of magnitude smaller than the typical size scales associated with particles like quarks. Given our current understanding, there is no evidence or theoretical basis to suggest that quarks have a size smaller than the Planck length.
It's important to note that our understanding of the nature of particles and the fundamental laws of physics is based on our best theories and experimental observations to date. However, there are still many open questions and areas of active research in physics, including the nature of particles at extremely small scales and the potential interplay between quantum mechanics and gravity. Advancements in future theories or experimental techniques may lead to a deeper understanding of these fundamental questions.