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Calcimator

Water Softener Sizing Calculator

Size a water softener based on water hardness, iron content, household usage, and regeneration frequency.

Inputs

GPG

NSF/ANSI 44: soft <1 GPG; moderately hard 3.5–7 GPG; very hard 7–10 GPG; extremely hard >10 GPG (>171 mg/L)

PPM
gallons
days

Results

Recommended Softener Size

40,000 grains

Monthly Salt Cost

$10.43

≈ 2 cups of coffee

Required Grain Capacity36,750 grains
Salt per Regeneration16 lbs
Annual Salt Usage834 lbs
How to Use This Calculator
  1. Enter your water hardness in grains per gallon (GPG) from a water test kit or report.
  2. Enter iron content in PPM — iron adds to the effective hardness demand.
  3. Set your daily water usage in gallons or enter the number of household members.
  4. Set the regeneration interval in days — 7 days is a common starting point.
  5. Review Required Grain Capacity and Recommended Softener Size to shop for the right unit.
  6. Use Annual Salt Usage and Monthly Salt Cost to estimate ongoing operating expense.

How the result changes with Daily Water Usage

Daily Water UsageRecommended Softener SizeMonthly Salt Cost
50064,000 grains$16.69
1,75096,000 grains$25.03
3,25096,000 grains$25.03
4,50096,000 grains$25.03

What each input means

Water Hardness
Water hardness in grains per gallon (GPG) per NSF/ANSI 44 (water softeners). 1 GPG = 17.1 mg/L = 17.1 ppm as CaCO₃. Soft: <1 GPG; slightly hard: 1–3.5 GPG; hard: 3.5–7 GPG; very hard: 7–10 GPG; extremely hard: >10 GPG.
Iron Content
Dissolved iron in parts per million. Each 1 PPM adds 5 GPG effective hardness to softener load.
Daily Water Usage
Household daily water usage. Average is 75 gallons per person per day.
Number of People
Number of people in the household. Used if daily usage is set to 0.
Regeneration Interval
Days between softener regeneration cycles. 7 days is typical for most households.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Water Hardness = 15, Iron Content = 0.5, Daily Water Usage = 300, Number of People = 4 = 5 input(s) provided
  2. Calculate Recommended Softener Size
    Recommended Softener Size
    40000 = 40000
  3. Calculate Monthly Salt Cost
    Monthly Salt Cost
    10.43 = $10.43
  4. Calculate Required Grain Capacity
    Required Grain Capacity
    36750 = 36750
  5. Calculate Salt per Regeneration
    Salt per Regeneration
    16 = 16

Engine last updated . Checked against 1 independently-derived test — how we verify calculators.

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