Water Softener Calculator
Calculate the grain capacity needed for a water softener based on water hardness, household usage, and regeneration frequency.
Results
Visualization
How It Works
Water softener sizing is based on how many grains of hardness the unit must remove between regeneration cycles. A family of 4 with 15 GPG hardness typically needs a 32,000-48,000 grain unit.
The Formula
Grain Capacity = Daily Gallons x Hardness (GPG) x Days Between Regen
Daily Gallons = People x 75 gal/person/day
Salt = Capacity / 3,000 grains per lb
Daily Gallons = People x 75 gal/person/day
Salt = Capacity / 3,000 grains per lb
Variables
- GPG — Grains Per Gallon — standard hardness measure
- 75 gal — Average daily water use per person
- 3,000 — Grains removed per pound of salt
Worked Example
4 people, 15 GPG, 7-day regen: 4 x 75 = 300 gal/day. 300 x 15 = 4,500 grains/day. 4,500 x 7 = 31,500 grains. Use 32,000 grain softener.
Practical Tips
- Get a water test before buying — don't guess hardness
- Iron in water requires extra capacity (add 5 GPG per 1 ppm iron)
- Demand-initiated regeneration saves salt vs timer-based
- Potassium chloride works as a salt alternative but costs 3x more