Water Hardness Converter
Convert between ppm, gpg, and other water hardness units
Conversion Formula:
gpg = ppm ÷ 17.1
Common Conversions
Water Hardness Classification
Soft (0-60 ppm): Treatment generally not necessary. Water may be slightly corrosive to pipes due to low mineral content. In some cases, water stabilization may be beneficial.
Moderately Soft (60-120 ppm): Minor treatment may be desired. Consider a basic carbon filter for taste improvement. Some scale prevention may be beneficial for hot water systems.
Hard (120-180 ppm): Water softener might be beneficial, especially for hot water systems and appliances. Ion exchange, salt-free conditioners, or template-assisted crystallization are common options.
Very Hard / Extremely Hard (180+ ppm): Water softener highly recommended to prevent significant scale buildup in pipes and appliances. Ion-exchange systems, reverse osmosis for drinking water, and regular descaling maintenance are advised.
Understanding Water Hardness
Water hardness refers to the mineral content in water, mainly calcium and magnesium ions. Hard water forms scale deposits in pipes and appliances and reduces soap efficiency.
Common Effects of Hard Water:
- Scale buildup in pipes, water heaters, and appliances
- White spots on glassware and fixtures
- Reduced soap lathering and cleaning effectiveness
- Dry skin and hair after washing
- Reduced efficiency of water heaters
- Shortened appliance lifespan
Water Hardness Comes From:
- Limestone and chalk (calcium carbonate)
- Dolomite (calcium magnesium carbonate)
- Gypsum (calcium sulfate)
- Groundwater passing through mineral deposits
- Dissolved minerals from rock formations
- Certain industrial processes
Types of Hardness:
- Temporary hardness: Can be reduced by boiling, caused by bicarbonates
- Permanent hardness: Cannot be removed by boiling, caused by sulfates and chlorides
Water Softening Methods
Soft Water (0-60 ppm)
Water stabilization
Add minerals or pH adjusters to prevent pipe corrosion
Basic filtration
Carbon filtration to improve taste
No treatment
Often no treatment is necessary for soft water
Moderately Hard (60-120 ppm)
Carbon filters
For taste and odor improvement
Magnetic water conditioners
Controversial method to prevent scaling
Template Assisted Crystallization
Converts hardness minerals to harmless crystals
Hard Water (120-180 ppm)
Ion exchange softeners
Removes calcium and magnesium ions by exchanging with sodium ions
Salt-free conditioners
Converts hardness minerals to crystals without removing them
Reverse osmosis
For drinking water, removes minerals through a membrane
Very Hard Water (>180 ppm)
Ion exchange softeners
Essential for preventing severe scaling issues
Sequestrants
Chemicals that keep hardness minerals in solution
Reverse osmosis
Complete mineral removal for drinking water
Descaling systems
Regular maintenance to remove existing scale
Regional Water Hardness Examples
North America
Europe
Asia & Oceania
Testing Methods
Home Testing:
- Water test strips (most common)
- Digital water hardness testers
- Soap test (shake water with soap to check lather)
- Home water test kits
Laboratory Testing:
- EDTA titration method (standard method)
- Ion chromatography (precise measurement)
- Atomic absorption spectroscopy (detailed analysis)
- ICP-MS (inductively coupled plasma mass spectrometry)
Hardness Classification Table
| Classification | mg/L CaCO₃ | gpg | °dH | °f |
|---|---|---|---|---|
| Soft | 0-60 | 0-3.5 | 0-3.4 | 0-6.0 |
| Moderately Soft | 60-120 | 3.5-7.0 | 3.4-6.7 | 6.0-12.0 |
| Hard | 120-180 | 7.0-10.5 | 6.7-10.1 | 12.0-18.0 |
| Very Hard | 180-250 | 10.5-14.6 | 10.1-14.0 | 18.0-25.0 |
| Extremely Hard | >250 | >14.6 | >14.0 | >25.0 |
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Visual Comparison
Hardness Scale (mg/L as CaCO₃):
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About the Water Hardness Converter
Convert between ppm, gpg, and other water hardness units All conversions run instantly in your browser and nothing you enter is sent to a server.
Common Conversion Formulas
| From | To | Formula |
|---|---|---|
| Parts per million (ppm) | Grains per gallon (gpg) | gpg = ppm × 0.058 |
| Parts per million (ppm) | Millimoles per liter (mmol/L) | mmol/L = ppm × 0.01 |
| German degrees (°dH) | Parts per million (ppm) | ppm = °dH × 17.848 |