Water softeners are available and sold in several sizes. Water softeners are rated by the number of grains of hardness they can remove from hard water. Softener units rated from 12,000 to 16,000 grains are considered small for a small family of 2 to 3 members; Softener units rated from 20,000 to 40,000 grains are considered medium-size units suitable for a medium family of say 4 to 6; and Softener units rated above 40,000 grains are considered large-capacity models suitable for large families of 6 or more members.
You can calculate the size of water softener your family needs by multiplying the number of family members in your household by 75. This will give you an idea of average number of gallons used per person per day and this will help you figure out how much water your household uses. Have a look at the Water Softener Capacity Chart below.
So, multiply number of family members in your household with 75 and then you multiply the resulting number by the number of grains per gallon (GPG) of hardness minerals present in the hard water. This way you can easily figure out the capacity a whole-house water softener you require.
For example, if there are 4 members in your family, multiply 4 x 75 = 300. Let us say your water has 10 GPG, then multiply 300 X 10 = 3,000 GPG. Therefore you need to remove 3,000 GPG each day.
Now you can compare this figure with the recharge cycle of the unit you are considering to buy to see how frequently regeneration must occur.
The whole idea behind selecting water softener size is to get a softener unit that will go at least 3 to 4 days between recharges. Always try to get a higher capacity water softener so that it can handle larger-than-normal water needs.