Interactive Calculator · 2026
Water Softener Size Calculator
Size a water softener from hardness and daily use. Enter the water treated per day, the hardness (get it lab-tested) and how many days you want between regenerations — get grains per gallon, the daily hardness load and the resin capacity to specify.
Required capacity → nearest standard resin size
Your water
Litres of hard water passing through the softener each day.
Hardness varies widely — get your supply lab-tested rather than guessing.
Fewer days means a smaller unit but more frequent salt-and-water regenerations.
Required capacity vs standard size
The recommended unit is the next standard resin size above your computed need.
Your softener must remove 23,176 grains of hardness between regenerations. Units are sold in standard resin sizes, so the next one up — a 24,000-grain softener — gives the working capacity plus headroom.
Higher hardness or more water means more frequent regeneration, which raises salt and water cost.
How this is calculated
- Grains per gallon = hardness ÷ 17.1 = 300 ÷ 17.1 = 17.54 gr/gal.
- Gallons per day = daily water ÷ 3.785 = 1,000 ÷ 3.785 = 264.2 US gal.
- Daily hardness load = grains/gallon × gallons/day = 17.54 × 264.2 = 4,635 grains/day.
- Required capacity = daily load × days between regeneration = 4,635 × 5 = 23,176 grains → next standard size 24,000 grains.
Indicative sizing for concept planning. Hardness varies — test your water first. Confirm the resin capacity, service flow and salt dose with the softener manufacturer before procurement.
Frequently asked questions
- How does the water softener size calculator work?
- It converts your water hardness in ppm to grains per gallon by dividing by 17.1, and converts your daily water in litres to US gallons by dividing by 3.785. Multiplying these gives the daily hardness load in grains, and multiplying that by the days you want between regenerations gives the total grains the softener must remove. It then rounds up to the next standard resin size.
- What inputs do I need and what values should I use?
- You need three things: the litres of hard water treated per day, the water hardness in ppm as calcium carbonate, and how many days you want between regenerations. Get hardness lab-tested rather than guessing, as Indian supplies vary widely. A typical home might treat 500 to 1500 litres a day and regenerate every 4 to 6 days; fewer days needs a smaller unit but more frequent salt and water use.
- How accurate is the recommended softener size?
- Treat it as indicative sizing for concept planning, not a final specification. The result rounds up to common resin sizes such as 16,000 to 64,000 grains to give working headroom. Actual capacity depends on salt dose, service flow rate and resin condition. Confirm the grain capacity, flow and salt setting with the softener manufacturer, and re-test your water if the supply source changes.
Related Guides — Deep-dive reading
Water Softeners in India: Beat Hard Water, Scale and White Spots
Why Indian groundwater is so hard, what a water softener actually does, how ion-exchange and salt regeneration work, where to place it (whole-house vs point-of-use), how to size it by hardness and usage, running cost, why softened water is not for drinking, and the alternatives worth knowing.
PlumbingSTP for Schools, Colleges & Universities: A Campus Design Guide
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