Guides Water Softener Sizing
Water Softener Sizing Four Steps and a Worked Example
Daily grains = people × gallons per person × hardness. Then pick a softener whose capacity at a moderate salt dose covers about a week of that.
Four Steps
- Get hardness in gpg. Divide mg/L (ppm) by 17.1.
- Add iron. 4 gpg per ppm of clear-water iron (Hydrotech manual).
- Grains per day. People × 75 gallons × compensated hardness.
- Match capacity. Look up capacity at each salt dose and pick the lowest dose that gives the interval you want.
Worked Example
Three people, 15 gpg, no iron: 3 × 75 × 15 = 3,375 grains a day. A week plus a day of reserve is about 27,000 grains.
| Softener at its low dose | Grains | Regenerates every | Salt per year |
|---|---|---|---|
| GE GXSH45W, 3.89 lb | 19,904 | 4.9 days | about 290 lb |
| Whirlpool WHES40, 3.4 lb | 17,300 | 4.1 days | about 300 lb |
| US Water Matrixx, 3 lb | 15,000 | 3.4 days | about 320 lb |
| Morton M30, 2.9 lb | 13,200 | 2.9 days | about 360 lb |
Our math from each maker’s published table. None reaches a 7-day interval at its lowest dose for this household, and that’s fine: the low dose still uses the least salt. Run your own.
Check the Flow Too
Capacity is half the job. A softener must also keep up with peak use. Use the certified service flow where there is one: 7.6 gpm for the WHES40, 9.5 for the GE, 10.8 for the Fleck 1.0 cu ft.
Common questions
What if I don't know my water use?
75 gallons per person per day is the planning figure in the Hydrotech and Aquasure manuals. Your water bill gives the real number.
Do I count iron?
Yes. The Hydrotech manual adds 4 gpg for each ppm of iron. US Water’s Matrixx manual adds a flat 5 gpg to the hardness setting.