Find the right water softener size for your home. Enter the number of people, daily water use, your water hardness in gpg or ppm and any iron, and see the grains you need to remove each day, the recommended capacity, how often it will regenerate and how much salt it uses.
Last updated:
Water use
gal/day
75 gal is a common sizing figure; use a water bill for your real use.
Water test
ppm
ppm
Softener settings
days
5–10 days is typical; most valves regenerate at least every 14 days.
lb
Enter your values to see the result.
Advertisement
Advertisement
How to use the Water Softener Size Calculator
Enter the people in the home and the water use per person (75 gal/day is a common sizing figure).
Enter your hardness from a water test or your utility's water quality report, and pick the unit.
Add iron and manganese if your test shows them; they count as extra hardness.
Choose how often you want it to regenerate and the salt setting.
Read the recommended size, then compare regeneration and salt use in the table.
Daily grains = people × gallons per person per day × compensated hardness
Capacity needed = daily grains × days between regenerations, compared with the effective capacity of each size at your salt setting.
Example: 4 people × 75 gal = 300 gal/day. Hardness 15 gpg plus 0.5 ppm iron × 4 = 17 gpg. Daily need = 300 × 17 = 5,100 grains; for 7 days 35,700 grains. At 9 lb/ft³ salt (≈25,000 grains per ft³) a 48,000 grain unit (1.5 ft³) gives 37,500 grains, so it regenerates about every 7.4 days.
Salt setting vs effective capacity
Salt dose
Grains per ft³ of resin (approx.)
32,000 grain unit (1 ft³)
48,000 grain unit (1.5 ft³)
Grains per lb of salt
6 lb/ft³
~20,000
~20,000
~30,000
~3,300
9 lb/ft³
~25,000
~25,000
~37,500
~2,800
12 lb/ft³
~28,000
~28,000
~42,000
~2,300
15 lb/ft³
~30,000
~30,000
~45,000
~2,000
Exact figures depend on the resin and valve; check the manufacturer's capacity chart. Lower salt settings use salt more efficiently but need more resin for the same days between regenerations.
Water hardness scale
Classification
gpg
ppm / mg/L
Soft
under 1
under 17
Slightly hard
1 – 3.5
17 – 60
Moderately hard
3.5 – 7
60 – 120
Hard
7 – 10.5
120 – 180
Very hard
over 10.5
over 180
Frequently asked questions
How do I calculate what size water softener I need?
Multiply people × gallons per person per day × hardness in grains per gallon to get the grains removed per day. Multiply by the number of days you want between regenerations (often 7). Choose a softener whose effective capacity at your salt setting meets that number. For 4 people using 75 gallons each at 15 gpg: 300 × 15 = 4,500 grains/day, or 31,500 grains a week.
How do I convert ppm hardness to grains per gallon?
Divide ppm (mg/L as calcium carbonate) by 17.1. For example, 257 ppm ÷ 17.1 ≈ 15 gpg. Going the other way, multiply gpg by 17.1.
Why does iron increase the softener size?
A softener uses the same resin capacity to remove dissolved iron and manganese as it does for hardness, and iron is harder to remove. A common rule is to add about 4 gpg of compensated hardness for every 1 ppm of iron (some dealers use 3 to 5).
What is the difference between nominal and effective softener capacity?
The nominal rating (for example 32,000 grains for 1 cubic foot of resin) is reached only at the maximum salt dose of about 15 lb per cubic foot. At an efficient 6 lb setting, the same resin removes only about 20,000 grains but uses far less salt per grain. That is why sizing should use the effective capacity at the salt setting you plan to use.
Is a bigger water softener better?
A bit oversized is good: it regenerates less often and can run at an efficient salt setting. A unit that is much too large may sit a long time between regenerations and needs adequate flow through the resin, so most installers aim for a regeneration every 5 to 10 days.
What water hardness needs a softener?
Water under about 1 gpg (17 ppm) is soft, 3.5–7 gpg is moderately hard, 7–10.5 gpg is hard and above 10.5 gpg (180 ppm) is very hard. Softeners are most useful from about 7 gpg upward, where scale and soap problems become noticeable.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.