As adults, the Oregon spotted frogs can range from about in snout-vent length which is the distance from the snout of the frog to the hide end/vent of the frog. Similar to most amphibians, the females tend to be larger than the males for reproductive reasons. The coloration of this species varies with age. As tadpoles, their back and tail musculature are brown and lack dark spotting, while the belly is a creamy white or aluminum color. Juveniles are usually some shade of brown, but may sometimes be olive green. Adult Oregon spotted frogs can be brown or reddish brown and tend to become increasingly red with age.