24 Volt Submersible Sump Pumps are designed to be submerged in the sump pit or in water. Used for many applications these pumps are often used in Solar House Pump set-ups. The standard 24V domestic sump pump pit size is 26 gallons and 18 inches diameter. In many cases the pit needs to be a minimum of 24 inches diameter and up to a depth of 36 inches. Based on the 18 inch diameter pit, to choose a pump size use a ruler and see how much water flows into your sump pump basin in 60 seconds. Every inch of water is equal to 1 gallon of water. If there is 6 inches of water in the pit you need a pump which will move 6 gallons of water per minute. (1 gallon = 3.78 litres).