Small yet powerful, the mini 25-watt Marina Submersible Aquarium Heater provides reliable heating for fresh or saltwater aquariums up to 20 litres (5.5 US gal) aquariums. The heater includes many practical features for easy use, safety and convenience, including an easy-to-access temperature set dial, on/off pilot light indicator, and a bumper guard for fish safety. Made of durable high-impact glass, its built to last under normal aquatic conditions. Approximately 6″.