Free Tool
Water Hardness Calculator
Enter your hardness number. See what it means for your home. Get the right softener size for your household.
How to Use This Tool
- Enter your hardness level. Find this number on your water test report. It may be listed as "hardness," "calcium carbonate," or "CaCO3." Switch between mg/L and GPG units.
- Select your household size. This determines what softener capacity you need.
- Read your results. See your classification, the impact on your home, estimated annual cost, and the recommended softener size.
Don't Know Your Hardness Level?
Order a water test that includes hardness. A basic panel costs $30–$80. Read our How to Read a Water Test Report guide for help understanding results.
Frequently Asked Questions
How do I convert mg/L to GPG?
Divide mg/L (ppm) by 17.1. For example: 171 mg/L ÷ 17.1 = 10 GPG. This calculator does the conversion automatically.
What hardness level needs a softener?
Most experts recommend a softener at 7+ GPG (120+ mg/L). At this level, scale buildup shortens appliance life. Some install at 3.5+ GPG for comfort.
How do I size a water softener?
Hardness (GPG) × people × 75 gallons/day × 7 days = weekly grain demand. Choose a softener that handles this in one weekly regeneration.