Calculator
Water Softener Size Calculator
Size a water softener from your household size and water hardness.
Verified August 2026
Grains per gallon. Your utility's water quality report lists this.
Recommended capacity
40,000 grains
Regenerating about once a week
- Daily softening load
- 5,600 grains
- Weekly softening load
- 39,200 grains
- Effective hardness
- 20 gpg
- Daily water use
- 280 gallons
Estimates only. Local pricing, site conditions and code requirements change the real number.
The formula
Daily grains = people x gallons per person x (hardness + iron penalty); Capacity = daily grains x 7 days
Size for a regeneration cycle of about every 7 days. Oversizing wastes salt on infrequent cycles; undersizing leaves hard water at the end of the week.
Worked example
A family of four on 20 gpg water needs roughly 44,800 grains of weekly capacity — a 48,000 grain unit.
Frequently asked questions
What size water softener do I need for a family of 4?
On typical 15–25 gpg water, a family of four needs a 40,000 to 48,000 grain softener to regenerate about weekly.
What is a good water hardness level?
Below 3 gpg is considered soft. Above 10 gpg is hard and causes visible scale on fixtures and inside water heaters.
Sources
Sources & verification
Last verified August 2026. Cost figures are modeled estimates based on national baselines adjusted for local labor and material pricing — they are not quotes. Permit rules change; confirm with the building department before starting work.