When figuring out water hardness, we will sometimes need to convert GPG to PPM. Both of these units determine how hard your water is. To help you out with the conversion, we have created the GPG to PPM calculator, complete with the GPG to PPM chart (with 0.1 to 50 GPG converted into PPM).
Note: In the conversion chart below, have denoted soft water (0-3.5 gpg) with this green color, moderately hard water (3.56-7.01 gpg) with this light blue color, hard water (7.06-10.51 gpg) with this blue color, and very hard water (10.57+ gpg) with this dark blue color.
Let’s first look at the units of water hardness we are dealing with here:
- GPG or Grains Per Gallon is the water hardness when 1 grain of calcium carbonate (64.8 mg of CaCO3) is dissolved in 1 US gallon of water. A US gallon is equal to 3.785412 liters of water.
- PPM or Parts Per Million is the water hardness when 1 mg of calcium carbonate (CaCO3) is dissolved in 1 liter of water. It is equal to mg/L unit for hard water.
As we can see, GPG is basically equal to 64.8 mg of CaCO3 per 3.785412 liters of water (US gallon). PPM is equal to 1 mg of CaCO3 per 1 liter of water. Based on this, we can use this formula to convert hard water GPG to PPM:
PPM = GPG × 17.118
Example: Let’s say that we have 25 GPG water hardness and would like to know how much is those 25 GPG in PPM. We just use the equation above like this:
PPM (25 GPG) = 25 × 17.118 = 427.95 PPM
As we can see, 25 GPG is equal to 427.95 PPM of water hardness.
Essentially, 1 GPG is equal to 17.118 PPM. For PPM to GPG conversion, you can check this similar PPM to GPG calculator and chart.
This was just one example. To help you out with the conversion, you can simply use the calculator or consult the GPG to PPM chart below the calculator:
GPG To PPM Calculator
Here you just insert the GPG, and the calculator will automatically convert that to PPM:
Let’s do one quick example to see how this calculator works. We want to convert 10 GPG to PPM. Just slide the slider to ’10’ and you get the result: 10 GPG is equal to 171.18 PPM.
Here is the full GPG to PPM chart with 0.1 GPG to 50 GPG water hardness converted into PPM units:
GPG To PPM Conversion Chart
| Grains Per Gallon (GPG): | Parts Per Million (PPM): |
| 0.1 gpg | 1.71 ppm |
| 0.2 gpg | 3.42 ppm |
| 0.3 gpg | 5.14 ppm |
| 0.4 gpg | 6.85 ppm |
| 0.5 gpg | 8.56 ppm |
| 0.6 gpg | 10.27 ppm |
| 0.7 gpg | 11.98 ppm |
| 0.8 gpg | 13.69 ppm |
| 0.9 gpg | 15.41 ppm |
| 1 gpg | 17.12 ppm |
| 1.5 gpg | 25.68 ppm |
| 2 gpg | 34.24 ppm |
| 2.5 gpg | 42.79 ppm |
| 3 gpg | 51.35 ppm |
| 3.5 gpg | 59.91 ppm |
| 4 gpg | 68.47 ppm |
| 4.5 gpg | 77.03 ppm |
| 5 gpg | 85.59 ppm |
| 5.5 gpg | 94.15 ppm |
| 6 gpg | 102.71 ppm |
| 6.5 gpg | 111.27 ppm |
| 7 gpg | 119.83 ppm |
| 7.5 gpg | 128.39 ppm |
| 8 gpg | 136.94 ppm |
| 8.5 gpg | 145.50 ppm |
| 9 gpg | 154.06 ppm |
| 9.5 gpg | 162.62 ppm |
| 10 gpg | 171.18 ppm |
| 11 gpg | 188.30 ppm |
| 12 gpg | 205.42 ppm |
| 13 gpg | 222.53 ppm |
| 14 gpg | 239.65 ppm |
| 15 gpg | 256.77 ppm |
| 16 gpg | 273.89 ppm |
| 17 gpg | 291.01 ppm |
| 18 gpg | 308.12 ppm |
| 19 gpg | 325.24 ppm |
| 20 gpg | 342.36 ppm |
| 21 gpg | 359.48 ppm |
| 22 gpg | 376.60 ppm |
| 23 gpg | 393.71 ppm |
| 24 gpg | 410.83 ppm |
| 25 gpg | 427.95 ppm |
| 26 gpg | 445.07 ppm |
| 27 gpg | 462.19 ppm |
| 28 gpg | 479.30 ppm |
| 29 gpg | 496.42 ppm |
| 30 gpg | 513.54 ppm |
| 35 gpg | 599.13 ppm |
| 40 gpg | 684.72 ppm |
| 45 gpg | 770.31 ppm |
| 50 gpg | 1855.90 ppm |
As you can see, the colors in the chart will mean different things; green for soft water, light blue for moderately hard water, blue for hard water, and dark blue for very hard water. This water hardness classification is based on these GPG and PPM water hardness scales:
- Below 3.5 GPG, we have soft water (that’s below 60 PPM).
- Between 3.56 and 7.01 GPG (that’s roughly between 61 and 120 PPM), we have moderately hard water.
- Between 7.06 and 10.51 GPG (that’s roughly between 121 and 189 PPM), we have hard water.
- At 10.57 GPG and above (that’s roughly 180 PPM and above), we have very hard water.
We hope that this illustrates well how to convert grains per gallon to parts per million hard water units. If you have any questions regarding this conversion, or would like for us to help you out, you can use the comment section below.