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What size water softener do I need?
Enter who lives there, how hard your water is and how often you want the softener to recharge. You get the grains it has to hold, the math line by line, and real softeners checked against it at every salt setting their makers publish.
Softeners checked against it
Every rating comes from the maker's own spec sheet or manual. A softener's grain rating depends on how much salt it uses each recharge, so each card lists every rating the maker publishes. The dark row is the lowest salt setting that covers your number.
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Where the numbers come from
The size comes from one line in North Dakota's water softener code (Administrative Code 62-04-08-06):
G x P x H x F = grains
- G, gallons each person uses a day. EPA WaterSense: "Each American uses an average of 82 gallons of water a day at home." The code itself uses 50 gallons; this tool starts from EPA's figure or your own bill.
- P, the people living there.
- H, hardness in grains per gallon. The code defines "one grain per gallon [17.1 milligrams per liter]", so a report in mg/L or ppm gets divided by 17.1.
- F, the days you want between recharges.
Penn State Extension does the same math in its softener guide: 75 gallons at 10 gpg for 4 people is 3,000 grains a day, so a 20,000-grain softener lasts about 6 to 7 days.
Iron. GE, Whirlpool and Morton print the same rule in their manuals: add 5 grains to the hardness for every 1 ppm of clear-water iron. The tool uses it and says so. It doesn't cover red-water or bacterial iron.
Salt. The same code says a rating "must be related to the pounds of salt required for each regeneration." That's why every card shows each rating with its salt.
Sources, retrieved October 30, 2026: North Dakota Admin. Code ch. 62-04-08 · EPA WaterSense statistics · Penn State Extension, Water Softening · USGS, Hardness of Water · UNL Extension NebGuide G1491 · each maker's spec sheet, linked on its card.
Questions
How do I figure out what size water softener I need?
Multiply the people in your home by the gallons each one uses a day, then by your hardness in grains per gallon. That's the hardness the softener pulls out each day. Multiply it by the days you want between recharges. North Dakota's softener code writes it as G x P x H x F.
How do I turn ppm or mg/L into grains per gallon?
Divide by 17.1. North Dakota's code defines one grain per gallon as 17.1 milligrams per liter, and GE's softener manual gives the same rule. 205 mg/L ÷ 17.1 = 12 gpg.
Why does one softener list three grain ratings?
Because the rating depends on the salt it uses per recharge. GE rates its GXSH40V at 11,700 grains with 2.3 lb of salt, 31,500 with 8.7 lb and 40,000 with 15.1 lb. The number in the name is the high-salt rating.
How much water does one person use a day?
EPA WaterSense says each American uses an average of 82 gallons a day at home. That counts outdoor water too, which EPA puts at more than 30 percent of household use on average. Your bill, divided by the days it covers and the people at home, gives your own number.
What if my water has iron?
GE, Whirlpool and Morton say to add 5 grains to the hardness setting for every 1 ppm of clear-water iron, and each lists the most iron its softener handles. Their manuals say these softeners won't remove red-water or bacterial iron. Above 5 ppm, the makers note that Wisconsin requires extra treatment, and UNL Extension says the extra iron can make a softener work less well. Get the water tested and talk to a water treatment pro.
How often should a softener recharge?
No official rule gives a target for automatic softeners. North Dakota's code says one shouldn't be sized to recharge more than once in 24 hours. Whirlpool's and Morton's controls let you force a recharge every 1 to 15 days. Each recharge uses water: 37 gallons at the highest salt setting for GE's GXSH40V, and about 50 gallons per UNL Extension.
Does softened water add sodium?
Yes. UNL Extension says softening adds about 8 mg/L of sodium for each grain per gallon of hardness, so 10 gpg water ends up near 80 mg/L. It says people on restricted sodium diets should account for it and consult their physician. Many homes leave a cold kitchen tap unsoftened for drinking and cooking.
| USGS class | mg/L | gpg (÷ 17.1) |
|---|---|---|
| Soft | 0 to 60 | 0 to 3.5 |
| Moderately hard | 61 to 120 | 3.6 to 7.0 |
| Hard | 121 to 180 | 7.1 to 10.5 |
| Very hard | more than 180 | more than 10.5 |