Water softener sizing calculator
Enter how many people live in the house and your water hardness from a test or the water report. You get the grains a day the softener removes, the size that regenerates about once a week, and how much salt it uses at the high and the efficient salt setting.
Inputs
Result
Every size for your house
Days between regenerations and salt a month at the full salt setting (about 18 lb per ft³) and the efficient one (6 lb per ft³).
| Softener | Resin | Days, full salt | Salt a month | Days, 6 lb | Salt a month |
|---|
How a water softener is sized
A softener is rated in grains: how much hardness it removes before it has to regenerate with salt. Four people using 75 gallons each a day with 15 gpg water put 4,500 grains a day through it, so a week between regenerations takes 31,500 grains of capacity.
Why the rating and the real capacity differ
Softeners are sold by a nominal rating of about 32,000 grains per cubic foot of resin: a 32,000 grain unit has 1 ft³, a 64,000 has 2 ft³. What the resin really delivers depends on how much salt each regeneration uses. At the practical maximum, about 18 lb per ft³, it is about 30,000 grains per ft³. At an efficient 6 lb per ft³ it is about 20,000.
So the 31,500 grains in the example need a 40,000 grain softener at full salt, where it uses about 82 lb of salt a month. A 64,000 grain softener does the same week at the 6 lb setting and uses about 41 lb a month. The bigger unit costs more up front and saves salt every month. A chart that matches the nominal rating straight to the weekly need would say 32,000, which at full salt runs about 6.7 days.
Water softener size chart
Softener size by people (rows) and hardness in gpg (columns), at 75 gallons a person a day, regenerating every 7 days at full salt. Size up one step for the efficient salt setting.
| People | 5 gpg | 10 gpg | 15 gpg | 20 gpg | 25 gpg | 30 gpg |
|---|---|---|---|---|---|---|
| 1 | 24k | 24k | 24k | 24k | 24k | 24k |
| 2 | 24k | 24k | 24k | 24k | 32k | 40k |
| 3 | 24k | 24k | 32k | 40k | 48k | 64k |
| 4 | 24k | 24k | 40k | 48k | 64k | 80k |
| 5 | 24k | 32k | 48k | 64k | 80k | 96k |
| 6 | 24k | 40k | 64k | 80k | 96k | over 96k |
| 7 | 24k | 40k | 64k | 80k | over 96k | over 96k |
| 8 | 24k | 48k | 80k | 96k | over 96k | over 96k |
Iron
A softener also removes small amounts of dissolved iron, and the iron uses up capacity. Add 5 gpg to the hardness for each ppm of iron: 1 ppm of iron in the example raises the need from 31,500 to 42,000 grains a week, a 48,000 grain unit. Higher iron levels, or iron that has already turned to rust, need an iron filter ahead of the softener.
Questions
What size water softener do I need for a family of 4?
At 15 gpg, four people need about 31,500 grains a week: a 40,000 grain softener at full salt, or 64,000 grains to run at the salt-saving 6 lb setting. Use your own hardness in the calculator.
What size water softener do I need for a family of 5?
At 15 gpg, five people need about 39,375 grains a week: a 48,000 grain softener at full salt, or 64,000 grains at the 6 lb setting.
What size water softener for a family of 3?
At 15 gpg, three people need about 23,625 grains a week: a 32,000 grain softener at full salt, or 40,000 at the 6 lb setting.
What size water softener do I need for a 4 bedroom house?
Size by the people who live there and the hardness, not the bedrooms. If you don't know how many will live in it, assume the house will be full and use the calculator with that number.
How do I convert ppm hardness to grains per gallon?
Divide by 17.1. Water at 171 ppm (or mg/L) as calcium carbonate is 10 gpg; 257 ppm is about 15 gpg.
Does a bigger water softener use more salt?
Not for the same water. Salt per regeneration goes up with the resin, but a bigger softener regenerates less often, and run at a lower salt dose it removes more hardness per pound. Oversizing a little and setting it to the efficient dose usually uses less salt.
How often should a water softener regenerate?
About once a week is the usual sizing target. A softener that is too small regenerates every day or two, using more water and salt; the calculator shows the days between regenerations for each size.
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