Water softener settings calculator
Your softener needs one number: how hard your water is, in grains. Set it too low and hard water slips through; too high and you waste salt every regeneration. Here's the exact number to program.
Setting = compensated hardness in grains per gallon (standard ion-exchange convention).
Water softener settings calculator
Enter your hardness and any iron to get the number to program into the softener.
Your softener's hardness setting is your water's hardness in grains per gallon, plus an allowance for any iron, rounded up to a whole number. Enter your hardness and iron below to get the number to program. For example, 18 grains with no iron is a setting of 18; iron raises it.
Reading the result
How to read your setting
The setting is simply your hardness in grains per gallon, plus an iron allowance, rounded up to a whole number. It tells the softener how much hardness each gallon carries, so it knows when the resin is spent and it's time to regenerate — the rinse cycle where the unit flushes captured minerals off the resin with salt brine and resets.
Set it on your true hardness, not above it: a padded setting makes the softener think it's working harder water than it is, so it regenerates early and wastes salt. Set it below and hard water breaks through before the cycle ends. The measured number is the honest input — look yours up if you don't know it.
Chart
Settings chart (no iron)
| Hardness (gpg) | Setting |
|---|---|
| 5 | 5 |
| 10 | 10 |
| 15 | 15 |
| 20 | 20 |
| 25 | 25 |
| 30 | 30 |
| 35 | 35 |
| 40 | 40 |
Iron
Why iron raises the setting
Iron uses up softening capacity just as hardness does, so it is added to the setting as extra grains — commonly three to five grains per part per million of iron. A water at 20 gpg with 3 ppm iron is programmed like 35 gpg at a factor of 5, or 32 at a factor of 4.
Levels
What “level 25” or “level 30” means
Some softeners label the setting a “hardness level” or just a dial number — and it's the same thing: your compensated hardness in grains per gallon. A level of 25 means the unit meters for 25-grain water; level 30 for 30-grain; level 50 for very hard water plus a heavy iron allowance.
So when a generic chart says “set level 30 for very hard water,” it's assuming 30 gpg — but you should program your measured number, not a band average. Match the level to your actual grains (plus iron) and the softener regenerates exactly when the resin is spent, neither early nor late.
Examples
Worked examples
Hardness 25 gpg, no iron. Nothing to add — the setting is your hardness rounded up, so program 25. That's the plain case: US water reports in ppm, but once you've converted to grains the number goes straight in.
Hardness 30 gpg, 1 ppm iron. Iron consumes capacity like hardness, so add it: at a factor of 5, that's 30 + (1 × 5) = 35 compensated grains, rounded up to 35. On a well with iron, this is why the number on the dial runs higher than your bare hardness.
Questions
Frequently asked
- What number should my water softener be set to?
- Your hardness in grains per gallon, plus an allowance for iron, rounded up. If your water is 18 grains with no iron, set it to 18.
- Why does iron raise the setting?
- Iron consumes softening capacity like hardness does, so each part per million of iron is added as extra grains — commonly three to five per ppm — before you set the number.
- What should hardness be set to for 25 gpg?
- With no iron, set it to 25. With iron, add roughly three to five grains per ppm of iron and round up.
Related: sizing · salt use · your area · the scale.
By Marko Visic, MPharm, BSc Physics. Source: Setting = compensated hardness (gpg), standard ion-exchange convention. Data last verified . Methodology.