dH/dGH To GPG Calculator: Convert dH To Grains Per Gallon (+ Chart)

Converting dH or dGH to GPG is not at all difficult. Because it does involve some math, we decided to simplify this conversion by creating an automatic dH to GPG Calculator. On top of that, we also converted 0.1-50 dH to GPG, and summarized all the results in a conversion chart (below the calculator).

Note: The conversion chart is color-coded based on the water hardness categorization: “Soft” water (0 – 3.50 GPG) is denoted with this green color, “Moderately Hard” water (3.51 – 7.01 GPG) with this light blue color, “Hard” water (7.02 – 10.51 GPG) with this blue color, and “Very Hard” water (10.52 GPG and above) with this dark blue color:

Now, let’s look at these water hardness units we are dealing with:

  • dH or dGH stands for degrees of Hardness or degrees of General Hardness. These are the same units (we will use them interchangeably), also known as German degrees. In essence, dH is defined as 10 mg/L CaO, and is equal to 17.848 PPM.
  • GPG are Grains Per Gallon. GPG is defined as 1 grain of CaCO3 per gallon; it is equal to 17.118 PPM.

In essence, we are converting degrees of Hardness to Grains Per Gallon. Here is the calculator that does this conversion automatically, followed by the conversion formula, and the all-encompassing dH to GPG conversion chart:


In order to demonstrate how this online calculator works, let’s solve the following example:

Say your water analysis says you have 12.5 dGH water hardness. How many GPG is 12.5 dGH?

To calculate that, we just slide the dH/dGH slider in the calculator above to ‘12.5’, and we get this result right away (screenshot):

converting dh to gallons per gallon water hardness units

We can see that 12.5 dH is equal to 13.03 GPG. On top of that, the calculator also tells us that this is considered “Very Hard” water, as per the standard water hardness scale chart here.

Note: If you need this conversion in reverse – converting grains per gallon to dH / dGH – you can check out our similar GPG to dGH calculator here.

Now, we can see that dH or dGH and grains per gallon (GPG) are very similar (they almost have 1:1 relationship). Let’s look at the conversion relationship before we check the useful conversion chart:

How To Convert dGH To GPG? (Formula)

When you compare the unit definitions (dH is 10 mg/L CaO, GPG is 1 grain or 64.8 mg per gallon), you can see that the conversion relationship here is the following:

1 dH = 1.042644 GPG

Basically, 1 dH is equal to 1.042644 grains per gallon (GPG). You have to admit, this is very close to 1:1 relationship (dH is by 4.3% bigger water hardness unit). From this, we can write the following dH to GPG formula like this:

GPG = dH × 1.042644

Essentially, if we want to convert dH to GPG, we have to multiply dH by 1.042644 factor. Let’s look at the 2nd example to see this equation in action:

How many GPG is 8 dH? 

Very simple. Just insert these 8 dH in the equation and calculate GPG like this (with result):

GPG (8 dH) = 8 dH × 1.042644 = 8.34 GPG

You can see that 8 dH is equal to 8.34 grains per gallon (GPG).

This is just one example. To help everybody out, we have taken degrees of Hardness ranging from 0.1 dH to 50 dH, and converted them to GPG. All the results are summarized in the following chart with the color-coding mentioned before (starting with “Soft” water, and proceeding to “Moderately Hard”, “Hard”, and “Very Hard” water, respectively):

dGH To GPG Conversion Chart

Here is the full conversion chart, accurate to 2 decimal points:

dH (degrees of Hardness or German Degrees): GPG (Grains Per Gallon):
0.1 dH 0.10 GPG
0.5 dH 0.52 GPG
1.0 dH 1.04 GPG
1.5 dH 1.56 GPG
2.0 dH 2.09 GPG
2.5 dH 2.61 GPG
3.0 dH 3.13 GPG
3.5 dH 3.65 GPG
4.0 dH 4.17 GPG
4.5 dH 4.69 GPG
5.0 dH 5.21 GPG
5.5 dH 5.73 GPG
6.0 dH 6.26 GPG
6.5 dH 6.78 GPG
7.0 dH 7.30 GPG
7.5 dH 7.82 GPG
8.0 dH 8.34 GPG
8.5 dH 8.86 GPG
9.0 dH 9.38 GPG
9.5 dH 9.91 GPG
10 dH 10.43 GPG
11 dH 11.47 GPG
12 dH 12.51 GPG
13 dH 13.55 GPG
14 dH 14.60 GPG
15 dH 15.64 GPG
16 dH 16.68 GPG
17 dH 17.72 GPG
18 dH 18.77 GPG
19 dH 19.81 GPG
20 dH 20.85 GPG
21 dH 21.90 GPG
22 dH 22.94 GPG
23 dH 23.98 GPG
24 dH 25.02 GPG
25 dH 26.07 GPG
26 dH 27.11 GPG
27 dH 28.15 GPG
28 dH 29.19 GPG
29 dH 30.24 GPG
30 dH 31.28 GPG
35 dH 36.49 GPG
40 dH 41.71 GPG
45 dH 46.92 GPG
50 dH 52.13 GPG

You can read all the most commonly used dGH to grains per gallon conversions from this chart. From the color coding, you can also see that:

  • “Soft” water is in the 0 – 3.36 dH range (same as the 0 – 3.5 GPG range).
  • “Moderately Hard” water is in the 3.37 – 6.72 dH range (same as the 3.51 – 7.01 GPG range).
  • “Hard” water is in the 6.73 – 10.08 dH range (same as the 7.02 – 10.51 GPG range).
  • “Very Hard” water has above 10.09 dH (same as above 10.52 GPG).

Using the calculator, the formula, and this conversion chart, you are now fully equipped to convert any dH to grains per gallon. If you need a bit of help, you are always welcome to use the comment section below, give us a few numbers, and we will do some math together.

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