Water Softener Size Chart: How to Find the Size Your Home Needs

A softener is sized in grains, and every water softener size chart starts from the same sum. Multiply the number of people in your home by the gallons each person uses in a day. Multiply that by your hardness in grains per gallon. The answer is how many grains your home makes in a day. Then you buy a unit that can hold about a week of it.

Buy too small and the unit has to clean itself more often. It uses more salt and more water to keep up. Buy too big and you paid for room you will never fill.

Nobody can pick the size for you from a brand name. It comes from your water and your household. Two numbers get you there.

Hardness is measured two ways. One is milligrams per liter. The other is grains per gallon, often written as gpg. Penn State Extension puts one grain per gallon at about 17 milligrams per liter.

Penn State groups hardness like this:

• Soft is under 1.0 gpg.
• Slightly hard is 1.0 to 3.5 gpg.
• Moderately hard is 3.5 to 7.0 gpg.
• Hard is 7.0 to 10.5 gpg.
• Very hard is over 10.5 gpg.

The Minnesota Department of Health says there is no rule that you have to soften your water. It calls the choice a personal one. It also says that above 7 grains per gallon, or 120 milligrams per liter, you might need a softener to keep your appliances working well.

Get your own number before you shop. A city water report will list it. On a well, a lab test or a test kit will.

The USGS puts indoor use at about 80 to 100 gallons per person per day. Penn State's own worked example uses 75 gallons per person per day.

Use your water bill if you have one. It beats any average. If you are on a well, 75 gallons per person is the figure the published guides use.

Here is Penn State's example, word for word in numbers. A home with 4 people, 75 gallons each per day, and 10 gpg water makes 3,000 grains a day. A unit rated 20,000 grains then cleans itself about every 6 to 7 days.

That gap matters. A softener that cleans itself every week is doing normal work. One that has to do it every day is too small for the house.

Fixr publishes a rule for this. Take the people in your home, times 75 gallons, times your hardness in grains per gallon, then times 10. The answer is the size to shop for.

Fixr's own example is a 3 person home with hardness of 15. That home needs a unit of roughly 35,000 grains.

Fixr also publishes a chart by household size. At 5 to 10 gpg, a home of 3 or 4 people lands at 32,000 grains. At 21 to 30 gpg, the same home lands at 40,000 grains. At 31 to 40 gpg, it lands at 64,000 grains.

The pattern is simple. More people or harder water moves you up one step. Both at once moves you up two.

Fixr lists unit prices by capacity. A 32,000 grain unit runs $400 to $1,000 for the unit alone. A 64,000 grain unit runs $1,000 to $1,500 for the unit alone.

The top pick in our own table is a 64,000 grain unit at $947. That sits inside the range Fixr publishes for that size, which is a good sign for a price you find online.

Buying one size up is not a mistake. It cleans itself less often and uses less salt doing it. Buying three sizes up is just money.

Three steps, in this order.

Step one is your hardness number. On city water, read the yearly water report or ring the utility and ask for the hardness. On a well, pay for a lab test. Penn State advises an independent lab rather than a free test from a company that also sells softeners.

Step two is the sum. People, times daily gallons, times hardness. Use your water bill for the gallons if you have one. Use 75 gallons per person if you do not.

Step three is the shopping list. Take your grains per day, multiply by 10, and shop for that number or the next size up. Then check the price against Fixr's range for that capacity, so you know if a quote is normal.

Write the three numbers down before you talk to anyone. A salesperson who names a size without asking for your hardness is guessing.