Aquarium Heater Size Guide

You should choose the appropriate heater wattage for your tank to ensure that the water is sufficiently heated and that the temperature remains constant throughout the entire tank. According to this chart below, I need a 50 watt heater for my 10 gallon tank (which I do have!) and a 75 watt heater for my 30 gallon tank (I have a 200 watt heater!!). The temperatures refer to the # of degrees of difference between your room temperature and the desired fish tank temperature. For example, my room temperature is 68 F, and my desired water temperature is 78 F. The difference is 10 F, so I look in the first column to see the required heater wattage.

Liters/Gallons (std tank size)	5ºC/9ºF	10ºC/18ºF	15ºC/27ºF
25 L/5 gal (1ft)	25 watt	50 watt	75 watt
50 L/10 gal (2ft)	50 watt	75 watt	75 watt
75 L/20 gal (3ft)	50 watt	75 watt	150 watt
100 L/30 gal (4ft)	75 watt	100 watt	200 watt
150 L/40 gal (6ft)	100 watt	150 watt	300 watt
200 L/50 gal(8ft)	150 watt	200 watt	two 200 watt
250 L/65 gal (10ft)	200 watt	250 watt	two 250 watt
300 L/75 gal	250 watt	300 watt	two 300 watt