Work out the grains per week your home needs, and the softener tier to check, from the number of people, your water hardness and any iron.
Disclaimer: All results are estimates for planning only. County and state rules govern — check with your local authority.
How to use this calculator
- Enter how many people live in the home.
- Enter your water hardness in grains per gallon (GPG). If you only have mg/L, use the Hardness Converter first.
- Enter iron in ppm if you know it, then read the grains per week and the recommended tier.
How the result is calculated
Weekly demand = people x 75 gallons per day x effective hardness (GPG) x 7 days. Effective hardness = hardness (GPG) + iron (ppm) x 4. Iron is counted at 4 GPG per 1 ppm as a stated assumption in this tool; sources vary between 4 and 5. The tool then picks the next tier above your weekly demand: 24,000, 32,000, 48,000, or 64,000 grains.
Worked example: 4 people, 10 GPG, 0 ppm iron = 4 x 75 x 10 x 7 = 21,000 grains per week, so the 24,000-grain tier.
Frequently asked questions
What is the difference between a 24,000 and a 32,000-grain softener?
It is capacity, not quality. A larger tier handles more grains between regenerations. If your weekly demand is close to a tier, choosing the next tier up is usually the safer planning choice.
How does iron affect softener size?
Iron adds to effective hardness in this tool, so the same water with iron needs a larger softener than the same hardness without iron. Very high iron may need separate treatment – ask a water professional.
My test shows mg/L, not GPG. What do I enter?
Convert first: GPG = mg/L / 17.1. For example, 171 mg/L / 17.1 = 10.00 GPG. The Hardness Converter does this for you.
Does a softener make water safe to drink?
No. A softener addresses hardness. It does not diagnose water safety. Use a qualified laboratory test for safety decisions, and follow local guidance.
How often will the softener regenerate?
That depends on actual water use, the tier, and the unit’s settings, so this sizing tool does not predict regeneration frequency. Follow the manufacturer’s and installer’s guidance.
When to call a professional
Call a water treatment professional if iron is high, you are on well water, you see staining or scaling damage, or you are unsure about hardness, iron, or plumbing compatibility.
Related tools: Hardness Converter – All free tools