SettingsSettings for this calculationUS
Number of people in the household.
Count everyone regularly using water in the home.
Your water hardness in grains per gallon (GPG).
Get this from a home test kit or your water utility's annual quality report. If given in mg/L or ppm, divide by 17.1 to convert to GPG.
How often you want the softener to regenerate.
Weekly regeneration is common for most households — less frequent regeneration needs a larger tank capacity.
Recommended softener capacity
24,000 grains capacity
This is a standard rule-of-thumb sizing method. Iron content, unusually high water use (irrigation, hot tubs), and manufacturer-specific efficiency ratings can shift the ideal size.
- Daily softening demand
- 2,250 grains/day
- Capacity needed before rounding
- 15,750 grains
They open the calculator with your figures already in it
Water Softener Sizing Calculator: 24,000 grains capacity — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Standard sizing formula: daily softening demand (grains) = people x 75 gallons/person/day x water hardness (grains per gallon); required capacity = daily demand x days between regenerations
- Common residential softener grain capacities: 24,000 / 32,000 / 48,000 / 64,000 / 80,000 grains
Inputs used
- Household Size
- 3
- Water Hardness
- 10
- Days Between Regenerations
- Every 7 days (weekly)
Intermediate steps
- Daily softening demand
- 2,250 grains/day
- Capacity needed before rounding
- 15,750 grains
Confidence note: This is a standard rule-of-thumb sizing method. Iron content, unusually high water use (irrigation, hot tubs), and manufacturer-specific efficiency ratings can shift the ideal size.
What this calculation does not cover
- The size it recommends is a nameplate grain rating, and nameplate ratings are measured at maximum salt dose. Run at the lower, more economical salt settings most units are actually set to, the same bed delivers materially fewer grains per cycle. The figure also holds back no reserve, while a metered valve starts a cycle before the bed is exhausted, so real intervals come out shorter than the days you picked.
- Water use is a flat 75 gallons (284 litres) per person per day, a planning convention rather than your household's measured consumption. Irrigation, a pool or hot tub top-up, a home business, or a second dwelling on the same supply are not in that figure. Two meter reads a fortnight apart with the irrigation off beat it.
- Only calcium and magnesium hardness is counted. Iron and manganese consume exchange capacity too and have to be added to the hardness figure by the equipment maker's own method; sediment, chlorine and extreme pH foul the bed or shorten resin life without changing this number at all.
- This is the grains side of the job only. It says nothing about the control valve's service flow rating, the pressure drop that costs when three fixtures run together, or the resin bed's own service flow limit — a tank with enough grains still passes hardness if water is pushed through it too fast. The sizes it chooses from are common single-tank residential ratings; twin-tank and commercial units are outside it.
- This is not a compliance check. Brine discharge to a septic system or sewer is restricted or banned in some jurisdictions, the drain line carries its own air gap and sizing requirements, and softening adds sodium to the treated water in proportion to the hardness removed — none of that is in this calculation.
Add the equipment this sizes
This result is a specification — 24,000 grains capacity — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations2
- Standard sizing formula: daily softening demand (grains) = people x 75 gallons/person/day x water hardness (grains per gallon); required capacity = daily demand x days between regenerations
- Common residential softener grain capacities: 24,000 / 32,000 / 48,000 / 64,000 / 80,000 grains
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