Water Softener Size Calculator and Installation Cost

How to use the water softener calculator

1. Enter hardness in grains per gallon (gpg) or mg/L, whichever your test report uses. City water reports usually list it in mg/L as calcium carbonate.
2. Add iron in ppm (same as mg/L) if your report shows it. Iron uses up softener capacity, so it is added to the hardness.
3. Enter people and daily use. 75 gallons per person is the planning figure from Penn State Extension. If you know your actual use from a water bill or meter, enter that instead.
4. Choose days between regenerations and a salt setting. Seven days at full salt is the default.
5. Pick single or dual tank and the install extras to see the cost.

How a softener is sized

Penn State’s example is a family of four using 75 gallons each per day with 10 gpg water. That is 300 gallons and 3,000 grains of hardness a day. A softener that removes 20,000 grains between regenerations would recharge every six to seven days.

Our calculator runs the same family on a seven-day cycle: 3,000 × 7 = 21,000 grains, so the smallest standard size that covers it is a 24,000-grain unit. That softener actually lasts about eight days between regenerations, about 46 a year.

Sources disagree a little on the cycle. HomeGuide multiplies daily use by 3 to 7 days, the Charger Water worksheet uses 3, and Alberta Agriculture’s table assumes a regeneration about every three days. A shorter cycle gives a smaller tank that regenerates more often. A longer one gives a bigger tank with more reserve, which is useful if the household grows or guests stay.

If hardness is in mg/L, divide by 17.1 to get gpg. NDSU Extension rounds this to 17. The USGS calls water of 61 to 120 mg/L moderately hard, 121 to 180 hard, and anything over 180 very hard. Alberta Agriculture suggests softening once hardness passes about 100 mg/L, or 6 gpg.

Iron and the salt setting

Ion-exchange resin removes dissolved (clear-water) iron as well as hardness, but it costs capacity. Marlo’s dealer manual adds 2 gpg for every ppm of iron; Charger Water’s worksheet multiplies ferrous iron by 4. The calculator defaults to 3 and lets you pick either end. Charger notes that standard softeners can usually remove up to about 2 ppm of clear-water iron. Above that, or if the water comes out of the tap rusty, ask a dealer about a dedicated iron filter.

Salt per regeneration sets how much of the resin’s rated capacity you get back. Marlo gives about 30,000 grains per cubic foot of resin at 15 lb of salt, and about 20,000 grains at 6 lb. The lower setting uses roughly 40% less salt per grain removed but needs a larger tank, and Marlo does not recommend the reduced setting when there is iron.

For a family of four at 15 gpg on a seven-day cycle, full salt calls for a 32,000-grain softener and about 820 lb of salt a year. The efficient setting needs a 48,000-grain unit but only about 490 lb of salt.

What a water softener costs

Unit prices are Angi’s, and Angi adds $150 to $1,000 for installation. HomeGuide puts a typical salt-based softener at $1,200 to $3,800 installed and a dual-tank system at $1,700 to $5,000. A dual-tank system lets one tank regenerate while the other is in service, so there is always soft water. HomeGuide also lists $250 to $900 for a dedicated electrical circuit if there is no outlet nearby, and $130 to $200 for a professional water test. Angi prices new pipe at $0.50 to $8 per foot when the softener can’t sit near the main line.

Running costs are mostly salt. Angi lists 40 lb bags of salt at $5 to $10, and potassium chloride at $50 to $70. The Penn State family above would use about 550 lb of salt a year at full salt, 14 bags.

Sodium and regeneration water

A softener swaps hardness for sodium. NDSU and Nebraska Extension both put the increase at about 8 mg/L of sodium for every gpg removed, so 10 gpg water gains about 80 mg/L. People on a sodium-restricted diet can use potassium chloride, or leave a cold tap unsoftened for drinking. Each regeneration also flushes about 50 gallons of water to the drain, according to Penn State and Nebraska Extension. The calculator multiplies that by the number of regenerations to show the yearly total.

How the estimate compares with other sources

The installed cost is built from unit prices plus labor for the size the calculator picks, and the headline is the midpoint of that range. Whole-job averages from other sources read on Oct 27, 2026 run higher: HomeGuide $2,500 on average ($1,200 to $3,800), Angi $1,500 ($200 to $6,000) and Fixr $2,500 ($1,100 to $3,000, for a dual-tank system in a 3–4 bedroom home). A basic single-tank job sized for a small household can sit below those averages; dual-tank systems, new plumbing runs or a new circuit move it up. These are national figures and prices vary by region.

Sources & assumptions

How this calculator gets its numbers. Full method: our methodology.

• Grains per day = people × gallons per person × compensated hardness. The default 75 gallons per person is the Penn State Extension figure; Charger Water’s worksheet also uses 75, and Marlo uses 60.
• Compensated hardness = hardness (gpg) + iron (ppm) × an allowance. Published allowances range from 2 (Marlo) to 4 (Charger Water) gpg per ppm; our default of 3 sits in the middle. Hardness in mg/L is converted at 17.1 mg/L per gpg.
• Capacity needed = grains per day × days between regenerations. HomeGuide multiplies by 3 to 7 days; we default to 7. Rated capacity assumes full salting (about 30,000 grains per ft³ of resin at 15 lb of salt); the efficient setting gets about 20,000 grains per ft³ from 6 lb (Marlo).
• Salt per year = grains per day × 365 ÷ grains per lb of salt (2,000 at full salt, about 3,333 at the efficient setting). Regeneration water assumes about 50 gallons per regeneration (UNL, Penn State). Sodium added ≈ 8 mg/L per gpg of hardness removed (NDSU, UNL).
• Costs are national estimates that vary by region: unit price by capacity and installation labor from Angi (August 2026), dual-tank systems, electrical circuits and water tests from HomeGuide (July 2025).

Sources

1. Fixr, How Much Does It Cost to Install a Water Softener?. Updated Jan 31, 2025: $1,100–$3,000, $2,500 national average (dual-tank system, 3–4 bedroom home).
2. Penn State Extension, Water Softening. 75 gallons per person per day; 4 people × 75 gal × 10 gpg = 3,000 grains per day, so a 20,000 grain softener regenerates every 6–7 days; about 50 gallons of water per regeneration.
3. Alberta Agriculture, Water Softening (Agdex 716-D32). 1 ft³ of high-capacity resin removes about 30,000 grains; sizing table on a 3-day cycle; softening recommended above about 6 gpg.
4. Marlo Inc., Water Chemistry and Treatment. Compensated hardness = hardness + iron ppm × 2; 15 lb salt per ft³ ≈ 30,000 grains, 6 lb ≈ 20,000 grains; reduced salt not recommended with iron.
5. Charger Water Treatment, Water Softening Sizing Worksheet. 75 gallons per person; ferrous iron × 4; daily demand × 3 for the unit size; standard softeners handle up to about 2 ppm of clear-water iron.
6. North Dakota State University Extension, Water Softening (Ion Exchange), WQ1031. 1 gpg ≈ 17 mg/L; hardness classes; about 8 mg/L of sodium added per grain of hardness removed.
7. University of Nebraska–Lincoln Extension, Drinking Water Treatment: Water Softening (Ion Exchange), G1491. Sodium added at about 8 mg/L per gpg; about 50 gallons of water per regeneration; size depends on hardness, daily use and flow rate.
8. U.S. Geological Survey, Hardness of Water. 0–60 mg/L soft, 61–120 moderately hard, 121–180 hard, over 180 very hard.
9. Angi, How Much Does Water Softener Installation Cost?. Unit price by capacity, materials only (24,000 grains $300–$500 to 96,000 grains $1,700–$2,500); installation $150–$1,000; salt $5–$10 and potassium chloride $50–$70 per 40 lb bag; new pipe $0.50–$8 per linear ft.
10. HomeGuide, How much does a water softener cost?. Salt-based softener $1,200–$3,800 installed; dual-tank $1,700–$5,000; dedicated circuit $250–$900; water test $130–$200; daily grains × 3 to 7 days.

Last reviewed October 28, 2026. Installed prices vary by region, contractor and job conditions; a written local bid wins.