Water softener size chart
Each cell is the smallest standard softener (rated grains) that covers 7 days of softening, assuming 75 gallons per person per day and no iron. Have iron or different water use? Use the calculator.
Efficient salt setting (recommended for salt savings)
| People \ Hardness | 5 gpg | 10 gpg | 15 gpg | 20 gpg | 25 gpg | 30 gpg |
|---|---|---|---|---|---|---|
| 1 | 24,000 | 24,000 | 24,000 | 24,000 | 24,000 | 24,000 |
| 2 | 24,000 | 24,000 | 24,000 | 32,000 | 40,000 | 48,000 |
| 3 | 24,000 | 24,000 | 32,000 | 48,000 | 64,000 | 64,000 |
| 4 | 24,000 | 32,000 | 48,000 | 64,000 | 80,000 | 110,000 |
| 5 | 24,000 | 40,000 | 64,000 | 80,000 | 110,000 | 110,000 |
| 6 | 24,000 | 48,000 | 64,000 | 110,000 | 110,000 | 110,000+ |
Full salt setting (maximum capacity)
| People \ Hardness | 5 gpg | 10 gpg | 15 gpg | 20 gpg | 25 gpg | 30 gpg |
|---|---|---|---|---|---|---|
| 1 | 24,000 | 24,000 | 24,000 | 24,000 | 24,000 | 24,000 |
| 2 | 24,000 | 24,000 | 24,000 | 24,000 | 32,000 | 32,000 |
| 3 | 24,000 | 24,000 | 24,000 | 32,000 | 40,000 | 48,000 |
| 4 | 24,000 | 24,000 | 32,000 | 48,000 | 64,000 | 64,000 |
| 5 | 24,000 | 32,000 | 40,000 | 64,000 | 80,000 | 80,000 |
| 6 | 24,000 | 32,000 | 48,000 | 64,000 | 80,000 | 110,000 |
Worked example: 4 people × 75 gal × 15 gpg = 4,500 grains/day × 7 = 31,500 grains. At full salt a 32,000-grain unit covers it; at the efficient setting (24,000 usable) you need the 48,000-grain size (36,000 usable). Lowe's works a similar example with 80 gallons per person: 4 × 80 × 15 = 4,800 grains/day, 33,600 per week, so a 40,000-grain unit (Lowe's Water Softener Sizing Chart (75–80 gal/person/day)).
Capacity by tank size
| Mineral tank | Rated (full-salt) grains | Usable at efficient salt setting |
|---|---|---|
| 8" x 44" | 24,000 | 18,000 |
| 9" x 48" | 32,000 | 24,000 |
| 10" x 44" | 40,000 | 30,000 |
| 10" x 54" | 48,000 | 36,000 |
| 12" x 48" | 64,000 | 48,000 |
| 13" x 54" | 80,000 | 60,000 |
| 14" x 65" | 110,000 | 84,000 |
Source: Nelsen Corporation, Softener Sizing Calculator (tank size vs. grain capacity table) (checked 2026-10-27). Brands differ; check your model's spec sheet.
Hardness scale
| USGS class | mg/L (ppm) as CaCO₃ | Grains per gallon (÷ 17.1) |
|---|---|---|
| Soft | 0–60 | 0.0–3.5 |
| Moderately hard | 61–120 | 3.6–7.0 |
| Hard | 121–180 | 7.1–10.5 |
| Very hard | over 180 | over 10.5 |
Classes: U.S. Geological Survey, Hardness of Water (checked 2026-10-27). Conversion: Maryland Geological Survey: 1 gpg = 17.118 mg/L.
Why the salt setting matters
Resin regenerated with 15 lb of salt per cubic foot holds about 30,000 grains; at 6 lb it holds about 20,000 (Excalibur Water, C800X10 softening resin: 30,000 grains/cu ft at 15 lb salt, 20,000 grains at 6 lb). That's two-thirds of the capacity for 40% of the salt, which is why many installers size up and run the efficient setting.