What Size Water Softener Do I Need?

Angi's sizing method takes four steps:

1. Find your hardness in grains per gallon (gpg). Utility reports often list hardness in mg/L or ppm. "To convert mg/L to GPG, divide by 17.1." If your water has iron, Angi says to add 3 gpg for every 1.0 ppm of iron.
2. Find your daily water use. Divide your average monthly water use in gallons (from your water bill) by 30.5. If you do not have that number, Angi says "you can multiply the number of people in your household by 90 gallons." For comparison, the EPA's WaterSense program has put the average at 88 gallons per person per day at home.
3. Multiply hardness by daily use. That gives the grains of hardness your softener has to remove each day.
4. Size for a week, plus a margin. "Look for a water softener that can handle a week's worth of your household's water consumption before regenerating," and "aim for a capacity that's 30% higher than your weekly softening requirement."

In short: hardness (gpg) × gallons per day × 7 days × 1.3, then round up to the next standard size.

Angi calls 32,000 grains "the most common size for a household of three to four people." That holds for moderately hard water. In harder water, the same family needs more capacity.

Here is the math for a family of four using 90 gallons per person per day (360 gallons a day), at three hardness levels:

The same family can need a softener twice the size depending on the water at their tap. That is why the size should come from a test of your water, not a city average.

Use the table above as a starting point, then round up, not down. Getting the size wrong costs you either way:

• Too small: "If your softener's too small, it'll regenerate too often, wasting salt and water," according to Bob Vila. HomeGuide adds that "undersized systems regenerate more frequently, increasing salt usage and reducing the system's lifespan."
• Too big: Bob Vila says an oversized softener "won't cycle often enough."

Larger households, homes with iron, and homes with very hard water all push the number up, which is why standard sizes run as high as 96,000 grains.

"The average household needs 40 pounds of water softener salt per month to effectively soften water," according to Angi. Your number depends on how hard your water is and how much you use: harder water and more people mean more regenerations, and each regeneration uses salt.

The softener itself matters too. The EPA says salt efficiency "is measured in grains of hardness removed per pound of salt," and that "greater salt efficiency reduces the amount of salt that needs to be purchased." The EPA recommends models with demand-initiated regeneration and "higher salt efficiency."

Angi says to check the salt level every four to six weeks and that you will typically "need to refill the water softener salt once every six to eight weeks." Angi recommends keeping salt at "at least 25% of the brine tank."

A softener that runs out of salt cannot recharge its resin, so check the brine tank on a schedule rather than waiting for hard water to come back.

Hardness varies across the metro, so the right size does too. Here is what local utilities report:

The Water Quality Association calls 7 to 10.5 gpg hard and anything above 10.5 very hard. The North Texas Municipal Water District notes that hardness "may be higher or lower at different times of the year."

What we measure at the tap can run higher than the utility reports. In homes we have tested in Frisco, McKinney, Prosper, Celina, and Forney, we have measured 11 to 16 grains per gallon or more, which is hard to very hard.

Test your water. Sizing depends on your actual hardness, any iron in the water, and how many people live in the house, and a city average can be off in either direction.

TAC offers a free in-home water test across Dallas-Fort Worth. We test your water, tell you how hard it is, and size a softener to your home before you decide anything.