What size water softener do I need?
People × 75 gallons × your hardness. Pick one that lasts about a week.
Multiply the people in your home by 75 gallons a day, then by your water hardness in grains per gallon. Pick a softener that covers about a week of that.
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You're probably on this page because:
- You're stuck between 32,000 and 48,000 grain
- You have a quote but no idea if the size makes sense
Here's the math, with real examples.
The formula
- People × 75 gallons = daily water use
- Daily use × hardness (grains) = daily grains
- Daily grains × 7 = weekly grains
- Pick a softener whose real capacity covers a week
Size chart
| People | 7 grains | 10 grains | 15 grains |
|---|---|---|---|
| 1 to 2 | 24,000 | 24,000 | 32,000 |
| 3 to 4 | 32,000 | 32,000 to 48,000 | 48,000 |
| 5 to 6 | 48,000 | 48,000 | 64,000 |
| 7+ | 64,000 | 64,000 | Twin tank |
Sizes assume an efficient salt setting. [Confirm with owner.]
Example
4 people × 75 gallons × 10 grains = 3,000 grains a day, or 21,000 a week. A 32,000 grain softener on an efficient setting gives roughly 20,000 to 24,000, so it fits.
Our take
Box capacity vs real capacity
We've answered this question thousands of times, on calls, on installs and for the water companies we supply.
The number on the box is usually capacity at the highest salt setting. At an efficient setting, real capacity is lower: roughly 20,000 grains per cubic foot of resin instead of 30,000+. Size to the real number and your softener won't recharge every few days.
Add about 5 grains of hardness for every 1 ppm of iron in your water, because iron uses up capacity too.
Written by people who install these every day
20+ years in water. No fluff, just how it really works.
- 20+ years in water
- Our own patents
- We supply other water companies
- [Thousands] of systems sold
- Licensed installers
Written by [Name], [title], [20+] years in water treatment. Reviewed by [Licensed plumber name], license # [#]. Last updated [date]. Sources: listed under each "By the numbers" block and linked in the copy
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Questions people ask
What size water softener for a family of 4?
Usually 32,000 to 48,000 grain, depending on hardness.
How big of a water softener do I need?
People × 75 gallons × hardness, sized to last about a week.
Is a bigger softener better?
No. Too big and it recharges too rarely.
What if I have iron?
Add about 5 grains per ppm of iron.
How do I find my hardness?
Your free ZIP report or a free test kit.
What if my water changes by season?
Size for the hardest months.