The short answer
At 15 gpg, four people need about 31,500 grains a week, so a softener rated about 42,000 grains or more; at 25 gpg, about 70,000.
By hardness
| Hardness | Grains a week | Rating to look for |
|---|---|---|
| 10 gpg | 21,000 | about 28,000 |
| 15 gpg | 31,500 | about 42,000 |
| 20 gpg | 42,000 | about 56,000 |
| 25 gpg | 52,500 | about 70,000 |
With iron
Add about 4 gpg per ppm of iron before you read the table: 15 gpg with 2 ppm of iron reads as 23 gpg.
Units that fit
Fleck 5600SXT 48,000-Grain Water Softener and Filter System, AFWFilters Fleck 5600SXT 48,000-Grain Water Softener, Aquasure Harmony Series AS-HS48D 48,000-Grain Water Softener. See the family shortlist.
Products mentioned
Softener and filter combo · Fleck
Fleck 5600SXT 48,000-Grain Water Softener and Filter System
48,000 grains · Fleck 5600 SXT
Whole-house softener · AFWFilters
AFWFilters Fleck 5600SXT 48,000-Grain Water Softener
48,000 grains · Fleck 5600sxt
Whole-house softener · Aquasure
Aquasure Harmony Series AS-HS48D 48,000-Grain Water Softener
48,000 grains · 12 GPM
Questions readers ask
Is a 48,000-grain softener enough for a family of four?
Yes up to about 20 gpg at an efficient setting; above that, size up.
What about a family of five?
Add about 7,900 grains a week per extra person at 15 gpg.