How many types of quarks are there in the standard model of physics?

The story behind the answer

There are six types (flavors) of quarks in the Standard Model: up, down, charm, strange, top, and bottom. They come in three generations—(up, down), (charm, strange), (top, bottom)—with charges of +2/3 for up-like quarks and −1/3 for down-like quarks. Due to color confinement, quarks aren’t observed alone; they bind into hadrons like the proton (uud) and neutron (udd).

Context and memory tip: masses increase across generations, with the top quark—discovered at Fermilab in 1995—being extremely heavy (~173 GeV). Remember the six with “Up, Down, Strange, Charm; Top, Bottom” or the initials U D S C T B.