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Whole House Water Softener Sizing: How to Match It to Your Hardness and Household
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Step 1: Get your hardness
Have the water tested by an independent lab (Penn State Extension). Hardness is measured in grains per gallon (gpg), and 1 gpg is about 17 mg/L. Penn State Extension says levels below 7.0 gpg will probably not cause major scaling and soap film. See the hardness table. Ask the lab for iron and pH too. Penn State Extension says oxidized iron clogs the resin, and that dissolved iron below 5 mg/L can usually be handled when pH is above 6.7 and hardness is 3 to 20 gpg.
Step 2: Estimate household water use
| Use | Gallons (Penn State Extension, Table 2) |
|---|---|
| Drinking and cooking | About 1 per person per day |
| Bathing | 25 to 60 per use |
| Dishwashing | 6 to 19 per use |
| Clothes washing | 20 to 33 per use |
Penn State Extension says to measure the water used at the hookups for each person in the household.
Step 3: Do the math
Penn State Extension's example: a softener with 20,000 grains of capacity, a household of 4, 75 gallons per person per day and hardness of 10 gpg.
- 75 gallons × 10 gpg × 4 people = 3,000 grains per day.
- 20,000 ÷ 3,000 = about 6 to 7 days between regenerations.
Use your own numbers. These are the example's numbers, not a recommendation for your home. We did not find an extension or government source on how large a reserve to add, so ask the installer what they allow for.
Step 4: Decide what it serves
Penn State Extension says toilets, outside spigots and basement sinks can be bypassed, while showers, sinks and laundry hookups should generally be softened. That cuts the water the softener handles and the salt it uses.
Step 5: Check the timing type
Penn State Extension says timed models regenerate whether the resin needs it or not, so they waste more water and salt. Demand-control models regenerate after a set number of gallons. Each regeneration uses about 50 gallons, which may overload a septic drainage field.
Size it, then compare
Get your hardness number from a lab first, then compare systems. A licensed water treatment professional or plumber can size and install one.
How to size a softenerSee whole-house softener optionsBrowse softeners on AmazonRelated guides
Common questions
How do I size a whole house water softener?
Penn State Extension's method: measure how much water each person uses, multiply by your hardness in grains per gallon and by the number of people to get grains per day, then compare that with the unit's capacity to see how often it must regenerate.
How much water does a person use a day?
Penn State Extension's worked example uses 75 gallons per person per day. Its table lists drinking and cooking at about 1 gallon per person per day, bathing at 25 to 60 gallons per use, dishwashing at 6 to 19 gallons per use and clothes washing at 20 to 33 gallons per use. Measure your own usage if you can.
What hardness number do I need?
Get a lab test. Penn State Extension says to have the water tested by an independent lab, because free dealer tests may not be third-party. Levels below 7.0 gpg will probably not cause major scaling and soap film.
Which taps should the softener serve?
Penn State Extension says toilets, outside spigots and basement sinks can be bypassed, while showers, sinks and laundry hookups should generally be softened.