How big is a adult seahorse?

The size of adult seahorses can vary depending on the species. On average, most adult seahorses range from approximately 1.5 to 30 centimeters (0.6 to 12 inches) in length. Some of the smallest species, such as the pygmy seahorse (Hippocampus bargibanti), may be as small as 1.5 centimeters (0.6 inches) in length, while larger species like the big belly seahorse (Hippocampus abdominalis) can grow up to 30 centimeters (12 inches) in length.