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Water TreatmentWQA Water Quality Standards

Water Softener Grain Sizing Calculator

Calculate required ion-exchange water softener grain capacity based on household family size, water hardness in grains per gallon (GPG), and iron content.

Water Softener Grain Sizing Calculator Technical Field Standard
Water Treatment Field StandardsWQA Water Quality Standards
Engineering formulations calibrated to IPC, UPC & NEC specificationsSub-Zero Cold Climate Tolerances

Quick Summary & Key Answer

To size a water softener: multiply household members by 75 gallons/day to get daily usage, multiply by compensated hardness (GPG + 5 per PPM iron) to get daily grain removal, and multiply by 7 days for weekly capacity. A family of 4 with 15 GPG hardness and 1 PPM iron produces 6,000 grains of daily hardness, requiring a 48,000-grain water softener.

  • 1 Grain Per Gallon (GPG) = 17.1 mg/L or PPM of calcium carbonate.
  • Water above 10.5 GPG is classified as 'Very Hard' by WQA.
  • Each 1.0 PPM of dissolved iron equals 5 grains of compensated hardness.

Interactive Calculator

Adjust inputs for real-time results

GPG

Test kit reading. 1 GPG = 17.1 PPM / mg/L.

PPM / mg/L

Add 5 GPG per 1.0 PPM of dissolved clear-water iron.

Calculated OutputWQA Sizing Verified

Recommended Softener Capacity

48,000 Grainsgrain capacity
Daily Hardness Removal Load
6,000 Grains/Day
Compensated Hardness (with Iron)
20.0 GPG
Estimated Daily Water Consumption
300 Gallons/Day
Estimated Salt Usage
~8-10 lbs per regeneration

Note: Sizing for a 7-day regeneration cycle prevents bacterial fouling and maximizes salt efficiency.

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Frequently Asked Questions

Common questions regarding this calculation and code compliance

A family of 4 with moderate to hard water typically needs a 32,000 to 48,000 grain capacity water softener.

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