Water softener size calculator: grain capacity and yearly salt cost

Use tested hardness × softened gallons per day × days between regenerations. Example values of 10 gpg, 4 people and 75 gallons per person per day give 3,000 grains per day and 21,000 grains for 7 days, before reserve. These are example values, replace with yours; no national water-use default is used. Verify capacity at the actual salt dose, peak flow, iron treatment and reserve with the manufacturer or installer. WQA Scale Deposits (undated; read 2026-10-02) gives 17.1 mg/L per gpg; WQA Getting Smart with Softeners (revised 2019; read 2026-10-02) discusses performance conditions.

People × softened gallons per person per day gives daily water use. At example values of 3 people, 60 gallons each and 171 mg/L hardness, measured hardness is 10 gpg, demand is 1,800 grains per day and 7 days needs 12,600 grains before reserve. Gallons per person per day is required; outdoor taps that bypass the softener do not count. The 17.1 mg/L conversion comes from WQA Scale Deposits (undated; read 2026-10-02).

Salt cost depends on daily demand, capacity at the actual salt dose and your bag price. At example demand of 3,000 grains per day and $8.97 per 40 lb bag, the EP42 rating pairs give idealized yearly salt estimates of 217.7 / 319.5 / 451.5 lb and $48.81 / $71.65 / $101.25. EcoPure EP42 manual p. 3 (rev. C 2023-10-20; read 2026-10-02) supplies 16,600 grains at 3.3 lb, 35,300 at 10.3 lb and 42,200 at 17.4 lb. The price is one store's price (Fleet Farm, observed 2 Oct 2026); enter yours (undated retailer price, Muskego pickup). These are idealized examples from one model's published test ratings, not a typical household, not three settings you pick; the controller varies the dose; real use can be higher. Cost is salt only.

Divide mg/L by 17.1 to get gpg (WQA Scale Deposits, undated; read 2026-10-02). EcoPure adds 5 gpg per ppm of dissolved clear-water ferrous iron (Iron Level Programming, updated 2026-03-17; read 2026-10-02); other makers differ, ask yours. At 10 gpg plus 1 ppm iron, the setting is 15 gpg. With 2 people × 80 softened gallons, demand is 2,400 grains per day. A paired rating of 32,000 grains at 8 lb salt gives 13.33 days, 219.0 lb salt per year and $35.59 per year at $6.50 per 40 lb bag. Blank iron means unknown; test for it.

Yes. Estimate, copy and print without an account. Web and MCP share 20 free calls per IP per UTC day and a global ceiling of 2,000 calls per UTC day. No separate tool cap. The calculation uses arithmetic without a model or live source lookup.