What Should Be the Water Softener Capacity Set As?

Set your water softener's capacity to what its resin actually delivers at the salt dose you use, not the number on the box. A "32,000-grain" softener only reaches that figure at its maximum salt setting; at an efficient dose it delivers closer to 20,000 to 25,000 grains. Then check that this capacity covers about a week of use: daily gallons times compensated hardness (gpg) times 7. If it does not, you need a larger softener or more frequent regeneration.

Grain Capacity Rating vs. Capacity Setting

Grain capacity is how many grains of hardness the resin can remove before it needs to regenerate. The rating on the box (32K, 48K, 64K) is the most the resin can hold when regenerated with a heavy salt dose, roughly 15 pounds per cubic foot of resin. Salt efficiency drops off sharply at high doses.

The capacity setting is what you tell the control valve. It should match the resin volume and the salt dose you actually program. Approximate figures for standard softener resin:

So a 1 cubic foot softener (sold as 32K) set at 6 pounds of salt should be programmed for about 20,000 grains, not 32,000. Set it too high and the valve thinks it has more soft water left than it does, so hard water slips through before regeneration.

How to Calculate the Capacity You Need

1. Measure your hardness in grains per gallon (gpg). If your report lists mg/L or ppm, divide by 17.1. Our ppm to grains per gallon converter explains how.
2. Add iron compensation. Add about 5 gpg for each 1 ppm of ferrous (clear-water) iron. This compensated hardness is also the number you enter as the hardness setting; see the ideal hardness setting for your softener .
3. Estimate daily water use. A common planning figure is about 75 gallons per person per day. See daily water use for a household of 5 .
4. Find daily grains. Multiply daily gallons by compensated hardness.
5. Multiply by 7. That is the capacity you need to regenerate about once a week. Then pick a resin volume and salt dose from the table above that delivers it.

Example

• 4 people x 75 gallons = 300 gallons per day
• 15 gpg hardness + 0.5 ppm ferrous iron (x 4 = 2 gpg) = 17 gpg compensated
• 300 x 17 = 5,100 grains per day
• 5,100 x 7 = 35,700 grains per week

A 1 cubic foot (32K) softener would need near-maximum salt and would still regenerate more than once a week. A 1.5 cubic foot (48K) softener at about 9 pounds per cubic foot (13.5 lb total) delivers roughly 37,500 grains, which covers a week at a reasonable salt dose. That is the better fit. Our water softener sizing guide walks through more examples.

Setting Capacity on a Metered Softener

A metered (demand) valve divides the capacity by your hardness to get the gallons it can treat, then subtracts a reserve. In the example above: 37,500 grains / 17 gpg = about 2,200 gallons. With a reserve of about one day's use (300 gallons), the valve regenerates after roughly 1,900 gallons, or about every 6 days.

• Reserve: keep about one day's water use in reserve so the softener does not run out before its overnight regeneration. Many valves calculate this automatically.
• Valve menus differ: some ask for capacity in grains, others ask for resin volume and salt dose and calculate capacity for you. Use the method your manual describes.

Common Capacity Setting Mistakes

• Using the box rating with a low salt dose. The softener runs out of soft water before it regenerates.
• Setting hardness too low or skipping iron. Same result: hard water bleeds through. Set hardness to your measured gpg plus iron compensation, not a generic number.
• Oversizing by a lot. A much bigger softener than you need regenerates rarely, which can let water channel through the bed. See whether it is OK to oversize a water softener , and our guide to the ideal regeneration interval in days .
• Ignoring flow rate. Capacity is not the only sizing factor; the softener also needs to keep up with peak flow. See how flow rates affect softener choice .

If Your Water Has Iron

Iron counts against capacity and fouls resin over time. The SoftPro Elite Smart HE for Well Water is rated for iron up to 3 ppm. Above 3 ppm, put the SoftPro AIO Iron Master in front of the softener so the softener only has to handle hardness. For city water, the SoftPro Elite Smart HE for City Water comes in 32K, 40K, 48K and 64K sizes.

Frequently Asked Questions