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Water hardness calculator
Make sense of a test result and plan your next step. Your readings stay in your browser.
Convert your hardness result
Enter total hardness from a tap test or your utility report. TDS and regional environmental samples are not substitutes for a tap hardness result.
Enter a nonnegative number up to 10,000 to see a conversion.
Conversion changes the units, not the precision of your test. Hardness describes minerals and is not a water-safety score.
Estimate softener working capacity
Use measured hardness above. Adjust these planning assumptions to your household; exclude outdoor water that bypasses the softener. This estimates hardness demand, not a recommended product.
Enter a hardness reading, a whole number of people, and valid water-use and regeneration values.
Compare this with the manufacturer’s usable capacity at its stated salt dose. Nominal capacity, peak flow, iron and manganese, and local discharge requirements need separate checks with your provider or installer.
Use the right number
Total hardness in this calculator is expressed as calcium carbonate (CaCO₃). One US grain per gallon is approximately 17.1 mg/L. The capacity calculation is GPG × daily softened water use × days, with one additional day as a visible reserve assumption.
For a dishwasher setting, convert your result to the unit in its manual and follow that model’s settings table. There is no universal dishwasher setting for a given hardness.
Classification source: USGS hardness of water.