Pacific treefrogs are a small, slender frogs with large toe pads. They have smooth skin that varies in color from light-brown to bright-green. Pacific tree frogs with red or brown backs also have been reported, but are thought to be rare. This species typically has darker markings on its body, including stripes on its dorsal surface and sides of its heads, which vary in intensity and in some individuals may be nearly absent. A dark triangular marking between the eyes is also common. Generally, a line of broken spots extends down the ventral surface to the groin area. The legs, arms, and feet are generally darker than the rest of the body. Within their natural range, Pacific treefrogs are the only frogs with padded toes and dark markings. Pacific treefrogs can change their body color depending on environmental conditions and need for camouflage to avoid predation. Recent research suggests that P. regilla changes color seasonally to match the presence or lack of green foliage. Color variation has also been associated changes in mean temperature. At high temperatures, these frogs often turn a shade of yellow. Under cooler temperatures, they return to their more typical darker colors. Males often are slightly different in color than females. Their upper body can be a dark gray olive color and may have a brown band extending through the eye and a yellow stripe along the upper lip. Females may be similar to males in color, but with little to no yellow stripe on the groin. During breeding season, it is easier to distinguish males from females by their different colored throats. Females have a smooth white throat while males have a dark brown or yellow throat with wrinkled skin.

Adult body size in Pacific treefrogs ranges from 2.5 to 4.8 cm. Mature females tend to be larger than males, which is not uncommon for anurans. Body mass of newly hatched tadpoles is, on average, 0.24. After 30 days, weight increases to between 0.35 and 0.45 g, which is more typical of adult Pacific treefrogs.

Pacific treefrogs, Sierran treefrogs, and Californian treefrogs were once considered a single species and referred to as Baja treefrogs (Pseudacris hypochondriaca). These species were later reclassified primarily due to differences in geographic ranges. These three species look very similar, except for the bumpy skin of the Sierran and Californian treefrogs.

Average mass: 0.35 g.

Range length: 2.5 to 4.8 cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; polymorphic

Sexual Dimorphism: female larger; sexes colored or patterned differently