Water Softener Size Calculator
No softening needed for this input
With 0 gpg hardness and no iron adjustment, there is no hardness load to remove — a salt-based softener is not solving a hardness problem at this input.
If your test really shows zero hardness but you still see scale, re-check units (gpg vs mg/L) or redo the test. See our water hardness test kit guide.
Your sizing result
Usable grains you need between regenerations: (rounded for display). We add a small buffer (about 10%), then suggest the common retail label whose usable capacity at an efficient salt setting covers that total — not the grain rating on the box.
How we got this
- Daily indoor use:
- Effective hardness:
- Daily hardness load:
- Capacity before regeneration: daily load × days between regenerations =
Control tip: Prefer metered (demand) regeneration over a fixed timer when you can — the softener regenerates based on use, not the clock. See our best water softener guide for context.
Related Filtiva guides
- Best water softener buyer’s guide — sizing, certification, salt vs salt-free
- Water hardness test kit guide — how to read gpg from a test
FAQ
What grains capacity do I need for a water softener?
Multiply your daily indoor gallons by your effective hardness in grains per gallon (hardness from your test plus optional iron adjustment), then multiply by the days you want between regenerations. Filtiva's rule of thumb is about 7 to 14 days. Compare that total with usable capacity at an efficient salt setting (about 6 to 8 lb/cu ft), not the grain rating on the box. A "32,000 grain" unit typically gives about 20,000 to 24,000 usable grains. This calculator adds a small buffer and maps to common retail labels.
Why does the calculator add extra hardness for iron?
A common trade practice is to add about 5 grains per gallon of hardness equivalent for each 1 ppm of iron so the softener is not undersized. Confirm details with your installer and water test.
Is 82 gallons per person per day accurate for my house?
It is a national average from EPA WaterSense for indoor use, not your exact home. A water bill or meter reading for indoor use is usually more accurate than multiplying people by 82.
Sources & notes
- 82 gallons per person per day — indoor-use average cited by EPA WaterSense
- Hardness (gpg) — use your lab report or home test; we do not invent test results
- Cubic feet to gallons — 1 cubic foot = 7.48 US gallons (utility conversion)
This tool is for planning only. Local water chemistry, iron pretreatment, resin settings, and installer practice can change what you buy.