Calculators / Water and gutters

What size water softener do I need?

Put in your water hardness and household. You get the grains you use a day, the softener size, the salt setting and how much salt a year.

Updated November 2026 · How we check our numbers

Softener size

1.5 cu ft of resin

Your water is very hard at 15 gpg. 4 people use about 4,920 grains a day, so 34,440 between regenerations. A 1.5 cu ft softener covers it at 11.8 lb of salt, regenerating about every 7 days.

Hardness: 15 gpgvery hard
A day: 4,920 grains
Per regeneration: 34,440 grains7 days
Salt: 615 lba year

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Estimate for planning only, not professional advice. Check the manufacturer’s instructions, your local code and a licensed professional before you buy, build or install. Use at your own risk. Terms.

a day = 4 × 82 gal × 15 = 4,920 grains

between regenerations = × 7 days = 34,440 grains

Capacity by tank and salt setting

Pentair whole-house softener manual

1 cu ft at 3.9 lb salt16,660 grains
Every 3 days
475 lb of salt a year
1 cu ft at 7.9 lb salt24,593 grains
Every 4 days
721 lb of salt a year
1 cu ft at 15.8 lb salt30,726 grains
Every 6 days
961 lb of salt a year
1.5 cu ft at 5.8 lb salt24,990 grains
Every 5 days
423 lb of salt a year
1.5 cu ft at 11.8 lb salt36,889 grains
Every 7 days
615 lb of salt a year
1.5 cu ft at 23.7 lb salt46,089 grains
Every 9 days
961 lb of salt a year
2 cu ft at 7.8 lb salt33,332 grains
Every 6 days
475 lb of salt a year
2 cu ft at 15.8 lb salt49,186 grains
Every 9 days
641 lb of salt a year
2 cu ft at 31.6 lb salt61,452 grains
Every 12 days
961 lb of salt a year

Set the hardness

Program the softener for 15 grains per gallon so it regenerates on time.

Water and salt

Lower salt settings remove more grains per pound but regenerate more often. Look for NSF/ANSI 44 certification; its efficiency rating means 5 gallons or fewer per 1,000 grains removed.

Sodium

Softened water carries a little added sodium. Anyone on a low-sodium diet should ask their doctor; a separate unsoftened tap or RO at the kitchen sink fixes it.

How we work it out

grains a day = people × gallons a person × (hardness in gpg + 5 × iron in mg/L)

Divide mg/L (ppm) by 17.1 for grains per gallon, as GE's softener manual says. GE and Pentair both say to add 5 to the hardness for every 1 mg/L of iron. EPA puts home use at 82 gallons a person a day; Penn State uses 75.

Multiply by the days between regenerations (Penn State's example comes out at 6 to 7, GE assumes 5) and pick the smallest softener that holds that many grains. Capacities by salt setting are from Pentair's whole-house softener manual: a lower setting is more salt-efficient but regenerates more often.

Where the numbers come from

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