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PPM to GPG Calculator: Water Hardness to Grains Conversion

According to research conducted by McGill University, water hardness is measured by the concentration of calcium carbonate per liter in parts-per-million (ppm). It is categorized as soft if less than 60 ppm, moderately hard between 60-120 ppm, and hard if it exceeds 120 ppm​.

This blog introduces user-friendly tools for this purpose: 


  1. PPM to GPG Calculator, 
  2. Detailed Water Hardness Conversion Table, 
  3. Manual conversion methods.

PPM to GPG Calculator

Simply the move counter to get the GPG for your PPM

PPM to GPG Water Hardness Table

Parts Per Million (PPM):Grains Per Gallon (GPG):Rating
1 ppm0.06 gpgSoft
5 ppm0.29 gpgSoft
10 ppm0.58 gpgSoft
15 ppm0.88 gpgSoft
20 ppm1.17 gpgSoft
25 ppm1.46 gpgSoft
30 ppm1.75 gpgSoft
35 ppm2.04 gpgSoft
40 ppm2.34 gpgSoft
45 ppm2.63 gpgSoft
50 ppm2.92 gpgSoft
55 ppm3.21 gpgSoft
60 ppm3.51 gpgSoft
65 ppm3.80 gpgModerately Hard Water
75 ppm4.38 gpgModerately Hard Water
80 ppm4.67 gpgModerately Hard Water
85 ppm4.97 gpgModerately Hard Water
90 ppm5.26 gpgModerately Hard Water
100 ppm5.84 gpgModerately Hard Water
110 ppm6.43 gpgModerately Hard Water
120 ppm7.01 gpgModerately Hard Water
130 ppm7.59 gpgHard Water
140 ppm8.18 gpgHard Water
150 ppm8.76 gpgHard Water
160 ppm9.35 gpgHard Water
170 ppm9.93 gpgHard Water
180 ppm10.52 gpgHard Water
190 ppm11.10 gpgVery Hard Water
200 ppm11.68 gpgVery Hard Water
250 ppm14.60 gpgVery Hard Water
300 ppm17.53 gpgVery Hard Water
350 ppm20.45 gpgVery Hard Water
400 ppm23.37 gpgVery Hard Water
450 ppm26.29 gpgVery Hard Water
500 ppm29.21 gpgVery Hard Water

Manual Conversion: Understanding the Math

While tools and tables are handy, knowing how to manually convert PPM to GPG can give you deeper insight into your water’s hardness. The process is simple:

  1. Understand the conversion factor: 1 GPG equals 17.1 PPM.
  2. Use the formula: GPG = PPM / 17.1.
  3. Apply the formula:

For example, to convert 100 PPM to GPG: GPG = 100 / 17.1 = approximately 5.85.


This method allows you to calculate the hardness of your water with just basic math, offering a great way to double-check your figures or make conversions on the fly.

Discovering Your Local Water Hardness

With water hardness affecting many U.S. homes, identifying your area’s level is key. Water hardness charts by state or city and local water authorities provide essential data. Visit this Amazing go-to resource on Water Hardness by state and zip-code

Tips for Accurate Water Hardness Measurement

Parts Per Million (PPM)Grains Per Gallon (GPG)Water Hardness Rating
0-60 Ppm0.00 - 3.51 GpgSoft Water
61-120 Ppm3.57 - 7.02 GpgModerately Hard Water
121-180 Ppm7.08 - 10.53 GpgHard Water
181+ Ppm10.58+ GpgVery Hard Water

FAQs for PPM to GPG Water Hardness Conversion

1. PPM to Grains Hardness Calculator:

An online tool converting water hardness from PPM to grains per gallon (GPG) for clarity on hardness levels.

2. Convert PPM Hardness to Grains per Gallon:

Use the formula GPG = PPM / 17.1 or an online calculator for instant and accurate conversions.

3. Difference Between PPM Hardness to Grains and PPM to GPG Hardness:

Both terms describe the same process of converting water hardness from PPM to GPG, measuring mineral content.

4. PPM to Grains of Hardness Meaning:

It's converting water hardness from parts per million (PPM) to grains of hardness, indicating mineral concentration.

5. GPG Meaning in Water:

GPG stands for grains per gallon, a measurement unit indicating water hardness based on mineral content per gallon.

6. Using an mg/L to GPG Calculator:

Enter the mineral concentration in mg/L to convert to grains per gallon (GPG), aiding in water treatment processes.

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