Key Takeaways:

• GPG (Grains Per Gallon): The industry-standard unit for measuring water hardness in the US.
• The Conversion: 1 GPG = 17.1 PPM (Parts Per Million) or mg/L.
• The Scale: Water over 10.5 GPG is considered "Very Hard." Most DFW cities test between 10 and 17 GPG.
• Why it Matters: Your water softener setting corresponds directly to your GPG number. If you get this number wrong, your system won't work.

If you've looked at a water quality report or shopped for a water softener, you've likely seen the acronym GPG. But what does it mean, and how does it relate to the "PPM" numbers you might see on a city report?

What is a "Grain" of Hardness?

"GPG" stands for Grains Per Gallon. It is an old unit of weight that is still the standard for the water treatment industry in North America. It specifically measures the amount of dissolved calcium and magnesium carbonate in one gallon of water.

Think of it literally: one "grain" is equal to about 1/7000th of a pound. It sounds small, but in water chemistry, it makes a huge difference.

GPG vs. PPM (Parts Per Million)

City water quality reports often list hardness in mg/L (milligrams per liter) or PPM (parts per million). These are essentially the same number.

To convert your city report to GPG (which is what your softener understands), use this simple math:

PPM (or mg/L) ÷ 17.1 = GPG

Example: If your city report says the hardness is 250 PPM: 250 ÷ 17.1 = 14.6 GPG

The Hardness Scale

Here is how water quality experts classify hardness:

Classification	Grains Per Gallon (GPG)	Parts Per Million (PPM)
Soft	0 - 1.0	0 - 17
Slightly Hard	1.0 - 3.5	17 - 60
Moderately Hard	3.5 - 7.0	60 - 120
Hard	7.0 - 10.5	120 - 180
Very Hard	Over 10.5	Over 180

Where Does DFW Fit?

Almost all municipal water in the Dallas-Fort Worth area falls into the "Hard" or "Very Hard" categories.

• Dallas/Fort Worth Core: Typically 7-10 GPG.
• Suburbs (Forney, Rockwall, Frisco, etc.): Typically 12-17 GPG or higher.

Why Your GPG Number is Critical

When we install a water softener, we program the computer valve with your specific hardness number.

• If set too low: The system won't regenerate often enough, and you'll get hard water breakthrough (spots on dishes, dry skin).
• If set too high: The system will clean itself too often, wasting salt and water.

Knowing your exact GPG is the secret to a system that works perfectly and efficiently.

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Reviewed by Sai Akash Tumu, TCEQ Licensed Water Treatment Specialist (#WT0007448). Our approach is to educate first. For a personalized assessment, contact us for a free consultation.

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Disclaimer: This guide is for informational purposes only. Water conditions vary, and we recommend a professional on-site water test for an accurate solution. This is not medical advice. Read full disclaimer >