Water softener size calculator

Enter your water hardness and household. You get grains per day and the smallest standard softener that covers a week between regenerations.

Picking a softener

Ion-exchange softener

Sized in grains of capacity. The figure on the tank is usually the maximum at a high salt setting, so many buyers go one size up for headroom and lower salt use.

Salt-free conditioner

Sized by flow rate and bathrooms rather than grains, since it does not remove minerals. It changes how scale forms, so this calculator does not apply to it.

Filter for drinking water

Carbon filters handle taste and chlorine. Reverse osmosis at the kitchen sink also removes hardness, but only for the water it treats.

Softener size chart

Smallest standard capacity for one regeneration a week at 75 gallons per person a day. A dash means even a 64,000-grain unit would need to regenerate more often.

Hardness	1 person	2 people	3 people	4 people	5 people	6 people
3 gpg 51 mg/L	24k	24k	24k	24k	24k	24k
5 gpg 86 mg/L	24k	24k	24k	24k	24k	24k
7 gpg 120 mg/L	24k	24k	24k	24k	24k	24k
10 gpg 171 mg/L	24k	24k	24k	24k	32k	32k
12 gpg 205 mg/L	24k	24k	24k	32k	32k	48k
15 gpg 256 mg/L	24k	24k	24k	32k	48k	48k
20 gpg 342 mg/L	24k	24k	32k	48k	64k	64k
25 gpg 428 mg/L	24k	32k	48k	64k	–	–

How the math works

A softener's capacity is the number of grains of hardness it can remove before it has to regenerate with salt. Daily load is hardness in grains per gallon times the gallons your household uses. Multiply by the days you want between regenerations, and pick the first size at or above that number.

Example: Los Angeles water is 7.1 gpg. Three people at 75 gallons each use 225 gallons, so the softener removes about 1,593 grains a day, or 11,151 a week.

If your water has iron, ask the dealer how to adjust: iron uses up capacity too, and the right allowance depends on the resin and the amount of iron.