A softener’s size is not about the size of your house. It is about how much hardness the softener has to take out of your water between cleanings. Two numbers decide it: how hard your water is and how much of it your household uses. This guide shows the method so you can check any size a pro suggests.
Install Water Softener is an independent referral service, not an installer or plumber. When you send the form, your details go to an independent local water treatment pro who can contact you and prepare a quote.
Number one: your hardness in grains per gallon
Softeners are rated in grains, so start with hardness in grains per gallon. If your report gives mg/L or parts per million, divide by about 17. So 170 mg/L is about 10 grains per gallon. City water customers find the figure in the utility’s yearly water quality report; well owners get it from a lab test. The signs of hard water guide explains both.
Number two: how much water you use
Your water bill or meter gives your household’s use, often in gallons or hundreds of cubic feet. Divide a month’s use by the days in the month for gallons per day. If it is in cubic feet, the utility can tell you the gallons. If you are on a well with no meter, a pro can estimate from the number of people, bathrooms and appliances.
The arithmetic
Multiply the two: grains per gallon times gallons per day gives the grains of hardness the softener removes each day. Then multiply by the number of days you want between regenerations. That is the capacity the softener needs, in grains.
| Step | Example | Your home |
|---|---|---|
| Hardness, grains per gallon | 16 (an example figure) | From your report or test |
| Water use, gallons per day | G (read your bill) | From your bill or meter |
| Grains removed per day | 16 x G | Hardness x use |
| Days between regenerations | D (ask the pro) | Set with the pro |
| Capacity needed, grains | 16 x G x D | Grains per day x days |
A softener’s capacity can depend on how it is set to regenerate, including its salt setting. That setting is a trade-off between salt use and how often the softener cleans itself. Ask the pro which setting they used and why.
What changes the answer
- Iron. EPA’s guideline for iron is 0.3 mg/L. Iron changes what the softener has to handle, so tell the pro your iron figure; it may change the size or call for a filter.
- More people later. If the household is growing, size for it.
- A range in your report. If hardness varies by source, size from the figure for your address, or the higher end if unsure.
- Water you do not soften. Outdoor taps left on hard water reduce the gallons the softener treats.
Why house size is the wrong question
People often choose a softener by square footage or number of bathrooms. Those are rough stand-ins for water use, and they can mislead. A large house with two people who are out all day may use less water than a small house with five. A home on moderately hard water needs far less capacity than the same home on very hard water. Utility reports range from water softened at the plant to about 10 grains per gallon to city water at 15 grains or more. Same household, different answer. That is why the method starts from your own two figures, not from the house.
Too small or too big
Too small, and the softener regenerates often and can let hard water through on heavy days. Too big, and you pay for capacity you do not use. The right size is the one worked out from your own figures, with the working shown.
Want a pro to size a softener from your figures?
Questions to ask about any size quoted
- What hardness and water use did you size from?
- How many days between regenerations does that give?
- What salt setting gives that capacity?
- Did you allow for iron?
- Is the unit certified to NSF/ANSI 44?
With these answers you can check the working yourself. The whole house installation page covers what comes after sizing.
Questions people ask
How big a water softener do I need for a 2,000 square foot house?
Floor area does not set the size. Hardness and water use do. Two homes of the same size can need very different softeners.
What size softener for a family of four?
Multiply your hardness in grains per gallon by the gallons your household uses a day, then by the days between regenerations. Your bill gives the use; your report or test gives the hardness.
