How much salt does a water softener use?

Q: How much salt does a water softener use?

A typical softener uses about 43 lb of salt a month for 3 people at 15 gpg. Tables by water hardness and household size, for salt and potassium, and how to work out yours.

About 43 lb a month for a household of three with 15 gpg water, which is about 13 forty-pound bags a year. Harder water and more people use more; the tables below cover the common range.

These are starting estimates for a typical 32,000-grain softener (1 cubic foot of resin) set to 9 lb of salt per regeneration, with each person using about 70 gallons a day. Your real use depends on your softener and its settings, which is why it's worth measuring: check how far the salt level drops over a few weeks.

Softener salt per month (sodium chloride)

Hardness	1 person	2 people	3 people	4 people	5 people	6 people
5 gpg	20 lb 6 bags/yr	20 lb 6 bags/yr	20 lb 6 bags/yr	20 lb 6 bags/yr	24 lb 7 bags/yr	29 lb 9 bags/yr
10 gpg	20 lb 6 bags/yr	20 lb 6 bags/yr	29 lb 9 bags/yr	38 lb 11 bags/yr	48 lb 14 bags/yr	57 lb 17 bags/yr
15 gpg	20 lb 6 bags/yr	29 lb 9 bags/yr	43 lb 13 bags/yr	57 lb 17 bags/yr	72 lb 22 bags/yr	86 lb 26 bags/yr
20 gpg	20 lb 6 bags/yr	38 lb 11 bags/yr	57 lb 17 bags/yr	77 lb 23 bags/yr	96 lb 29 bags/yr	115 lb 34 bags/yr
25 gpg	24 lb 7 bags/yr	48 lb 14 bags/yr	72 lb 22 bags/yr	96 lb 29 bags/yr	120 lb 36 bags/yr	144 lb 43 bags/yr
30 gpg	29 lb 9 bags/yr	57 lb 17 bags/yr	86 lb 26 bags/yr	115 lb 34 bags/yr	144 lb 43 bags/yr	172 lb 52 bags/yr

Potassium chloride per month

Potassium chloride softens less per pound, so you need about 25% more by weight.

Hardness	1 person	2 people	3 people	4 people	5 people	6 people
5 gpg	24 lb 7 bags/yr	24 lb 7 bags/yr	24 lb 7 bags/yr	24 lb 7 bags/yr	30 lb 9 bags/yr	36 lb 11 bags/yr
10 gpg	24 lb 7 bags/yr	24 lb 7 bags/yr	36 lb 11 bags/yr	48 lb 14 bags/yr	60 lb 18 bags/yr	72 lb 22 bags/yr
15 gpg	24 lb 7 bags/yr	36 lb 11 bags/yr	54 lb 16 bags/yr	72 lb 22 bags/yr	90 lb 27 bags/yr	108 lb 32 bags/yr
20 gpg	24 lb 7 bags/yr	48 lb 14 bags/yr	72 lb 22 bags/yr	96 lb 29 bags/yr	120 lb 36 bags/yr	144 lb 43 bags/yr
25 gpg	30 lb 9 bags/yr	60 lb 18 bags/yr	90 lb 27 bags/yr	120 lb 36 bags/yr	150 lb 45 bags/yr	180 lb 54 bags/yr
30 gpg	36 lb 11 bags/yr	72 lb 22 bags/yr	108 lb 32 bags/yr	144 lb 43 bags/yr	180 lb 54 bags/yr	216 lb 65 bags/yr

How the numbers work

Grains to remove a day = people × gallons per person × hardness (gpg). Iron counts too: add 4 gpg for each ppm of iron (15 gpg with 2 ppm iron uses about 66 lb a month for three people).
The softener regenerates when about 80% of its capacity is used, and at least every 14 days. At 9 lb per cubic foot, one cubic foot of resin holds about 25,000 grains.
Salt per month = salt per regeneration ÷ days between regenerations × 30.
If your hardness is in mg/L (ppm), divide by 17.1 to get gpg.
Light use has a floor: a softener still regenerates at least every two weeks to keep the resin fresh, so it uses about 20 lb a month however little water you use.
A timer softener regenerates every set number of days, so it uses a little more than the table when its setting is rounded down.

Know when yours will run out

Water Softener Buddy starts from exactly this estimate, then learns your household's real salt use from quick level checks and reminds you a few days before the tank is empty. It's free, works offline and needs no sensor.