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Understanding Water Hardness: Converting PPM to GPG

Updated: Nov 22

Alt Text Description: An illustration of a calculator with water droplets, representing the conversion between parts per million (ppm) and grains per gallon (gpg) for water hardness. The calculator symbolizes the conversion formula, gpg = ppm/17.118, indicating the relationship between the two units. This conversion is important for understanding and managing water hardness levels, especially for water softener systems.
Water Hardness PPM To GPG Calculator

Water hardness is an important factor to consider when it comes to water quality. In the United States, water hardness is commonly measured in two units: parts per million (ppm) and grains per gallon (gpg). These units help quantify the amount of calcium carbonate (CaCO3) dissolved in water, which is a key indicator of water hardness.


Parts per million, also known as American degrees, represents the concentration of CaCO3 in water. It signifies the number of milligrams of CaCO3 per liter of water. On the other hand, grains per gallon is another unit used to measure water hardness. It represents the number of grains of CaCO3 dissolved in a gallon of water.

Converting PPM to GPG

Converting ppm to gpg requires a simple calculation using a conversion factor. The conversion formula is as follows:

"gpg = ppm/17.118"

By dividing the parts per million value by 17.118, you can obtain the equivalent value in grains per gallon. The conversion factor, 17.118, accounts for the volumetric and mass differences between the two water hardness units. It signifies that every 1 gpg is equal to 17.118 ppm.

Conversion Tables Of PPG To GPG

Parts Per Million (PPM):

​Grains Per Gallon (GPG):

1 ppm

​0.06 gpg

2 ppm

​0.12 gpg

3 ppm

0.18 gpg

4 ppm

0.23 gpg

5 ppm

0.29 gpg

6 ppm

0.35 gpg

7 ppm

0.41 gpg

8 ppm

0.47 gpg

9 ppm

0.53 gpg

10 ppm

0.58 gpg

15 ppm

0.88 gpg

20 ppm

1.17 gpg

25 ppm

1.46 gpg

30 ppm

1.75 gpg

35 ppm

2.04 gpg

40 ppm

2.34 gpg

45 ppm

2.63 gpg

50 ppm

2.92 gpg

55 ppm

3.21 gpg

60 ppm

3.51 gpg

65 ppm

3.80 gpg

70 ppm

4.09 gpg

75 ppm

4.38 gpg

80 ppm

4.67 gpg

85 ppm

4.97 gpg

90 ppm

5.26 gpg

95 ppm

5.55 gpg

100 ppm

5.84 gpg

110 ppm

6.43 gpg

120 ppm

7.01 gpg

130 ppm

7.59 gpg

140 ppm

8.18 gpg

150 ppm

8.76 gpg

160 ppm

9.35 gpg

170 ppm

9.93 gpg

180 ppm

10.52 gpg

190 ppm

11.10 gpg

200 ppm

11.68 gpg

210 ppm

12.27 gpg

220 ppm

12.85 gpg

230 ppm

13.44 gpg

240 ppm

14.02 gpg

250 ppm

14.60 gpg

260 ppm

15.19 gpg

270 ppm

15.77 gpg

280 ppm

16.36 gpg

290 ppm

16.94 gpg

300 ppm

17.53 gpg

310 ppm

18.11 gpg

320 ppm

18.69 gpg

330 ppm

19.28 gpg

340 ppm

19.86 gpg

350 ppm

20.45 gpg

360 ppm

21.03 gpg

370 ppm

21.61 gpg

380 ppm

22.20 gpg

390 ppm

22.78 gpg

400 ppm

23.37 gpg

410 ppm

23.95 gpg

420 ppm

24.54 gpg

430 ppm

25.12 gpg

440 ppm

25.70 gpg

450 ppm

26.29 gpg

460 ppm

26.87 gpg

470 ppm

27.46 gpg

480 ppm

28.04 gpg

490 ppm

28.62 gpg

500 ppm

29.21 gpg

550 ppm

32.13 gpg

600 ppm

35.05 gpg

650 ppm

37.97 gpg

700 ppm

40.89 gpg

750 ppm

43.81 gpg

800 ppm

46.73 gpg

850 ppm

49.66 gpg

900 ppm

52.58 gpg

950 ppm

55.50 gpg

1000 ppm

58.42 gpg

Water Hardness Calculations

These are particularly relevant when it comes to water softener systems. These systems are designed to remove excess minerals from water, such as calcium and magnesium, which contribute to water hardness. By knowing the hardness level of your water in either ppm or gpg, you can determine the appropriate water softener system and settings to effectively treat your water.

Water softeners play a crucial role in reducing the negative effects of hard water. Excessive hardness can lead to mineral buildup in pipes and appliances, decreased lathering of soaps and detergents, and even skin and hair dryness. By installing a suitable water softener system, you can mitigate these issues and enjoy the benefits of soft water throughout your home.

Factors Influencing Water Hardness

Water hardness is not solely determined by calcium carbonate content; other factors also play a crucial role. Exploring the additional influences on water hardness, such as the presence of magnesium and other minerals, provides a more comprehensive understanding of the overall water quality.

Sustainable Approaches to Water Softening

Incorporating a sustainable approach to water softening is essential in today's environmentally conscious landscape. Aquawise stands out by providing eco-friendly water treatment solutions that not only mitigate water hardness but also align with sustainable practices.

In Conclusion

Understanding the conversion between ppm and gpg is essential for assessing water hardness levels and choosing the appropriate water treatment solutions. Whether you need to convert ppm to gpg or vice versa, the conversion formula of dividing by 17.118 provides a straightforward method. By considering water hardness and investing in a reliable water softener system, you can enhance the quality of your water and improve your overall daily living experience.

FAQs: Understanding Water Hardness: Converting PPM to GPG

What does PPM stand for in water hardness measurement?

PPM stands for "parts per million," also known as American degrees, representing the concentration of calcium carbonate in water.

What is the conversion formula for PPM to GPG?

The conversion formula is: "gpg = ppm/17.118." Simply divide the PPM value by 17.118 to get the equivalent value in grains per gallon.

Why is water hardness measured in both PPM and GPG?

Water hardness is commonly measured in both PPM and GPG to provide different units for quantifying the amount of calcium carbonate in water, offering flexibility in reporting and analysis.

How do I use the conversion tables for PPM to GPG?

Locate the PPM value in the table and find the corresponding GPG value. For precise conversions, use the conversion formula for calculations not listed in the table.

Why is water hardness relevant to water softener systems?

Water hardness is crucial for water softener systems as it helps determine the appropriate system and settings to effectively remove excess minerals like calcium and magnesium, preventing issues such as mineral buildup and improving water quality.

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