Softener size for 6 people, by water hardness
Based on 75 gallons per person per day and a 7-day cycle. Find your hardness from a test strip or your water report.
| Hardness | Grains per day | Per 7-day cycle | Softener size |
|---|---|---|---|
| 5 gpg | 2,250 | 15,750 | 16,000 grains |
| 10 gpg | 4,500 | 31,500 | 32,000 grains |
| 15 gpg | 6,750 | 47,250 | 48,000 grains |
| 20 gpg | 9,000 | 63,000 | 64,000 grains |
| 25 gpg | 11,250 | 78,750 | 80,000 grains |
| 30 gpg | 13,500 | 94,500 | Over 80,000 grains: consider two units |
If you also have iron in the water
Using 15 gpg water as the baseline:
| Iron | Grains per day | Softener size |
|---|---|---|
| 0 ppm | 6,750 | 48,000 grains |
| 1 ppm | 9,000 | 64,000 grains |
| 2 ppm | 11,250 | 80,000 grains |
| 3 ppm | 13,500 | Over 80,000 grains: consider two units |
Iron above a few ppm needs other treatment, as well as softening. See the water softener sizing guide for the details.
Want to change anything else? The calculator above is the full Water Softener Size Calculator: edit any number and the results update instantly.
Tools & materials for this project
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Frequently asked questions
What size water softener for 6 people?
At 15 grains per gallon of hardness and a weekly regeneration, 48,000 grains. It ranges from 16,000 grains at 5 gpg to Over 80,000: consider two units at 30 gpg.
How many grains does a household of 6 use per day?
About 6,750 grains per day at 15 gpg (6 × 75 gallons × 15). Divide by the hardness of your own water to adjust.
Does iron change the softener size for 6 people?
Yes. Each 1 ppm of iron adds about 5 gpg of effective hardness. At 2 ppm of iron in 15 gpg water, a household of 6 needs a 80,000 grain unit.
Related sizes and guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.