The common gudgeon has an elongated body. Its belly is flat and whitish. Its pectoral fins are quite broad and spread out, allowing it to cling to the bottom.
It has a pointed and narrow snout. Its tail fin is well forked. The body is grayish-green, speckled with brown on the back, sides, and fins. It is punctuated with seven to ten large dark spots on the sides, as well as seven to eight similar but smaller spots on the dorsal ridge.
The lateral scales are bluish in juveniles.