Convert mg/L To GPG Water Hardness: mg/L To GPG Calculator + Chart

Water hardness is sometimes expressed in mg/L (usually mg/L of CaCO3 or calcium carbonate). If you need to express water hardness GPG, you have to convert mg/L of calcium carbonate to GPG (Grains Per Gallon).

To help you out, we have created this mg/L to GPG calculator for water hardness, followed by a simple-to-use 0-1000 mg/L to GPG chart:

 

The key conversion rule we need to apply here is this:

1 mg/L is equal to 0.058418 GPG.

To convert mg/L (milligrams per liter) of calcium carbonate to grains per gallon, we need to multiply mg/L by 0.058418. Here is the mg/L to GPG formula:

GPG = mg/L × 0.058418

Quick Example: My water hardness is 100 mg/L of CaCO3. How many GPG is that? Just plug 100 mg/L into the above equation like this:

GPG = 100 mg/L × 0.058418 = 5.84 GPG

You can try this with the calculator above. You will see that 100 mg/L is equal to 5.84 GPG, and that this is considered “Moderately Hard” water.

Note: If you want to check out this conversion in reverse – GPG to mg/L – you can check this GPG to mg/L calculator.

We have converted a bunch of mg/L to GPG and summarized the results in a neat chart. This chart is also color-coded, based on the water hardness scale categorization: soft water (0-60 mg/L) is denoted with this green color, moderately hard water (61-120 mg/L) with this light blue color, hard water (121-180 mg/L) with this blue color, and very hard water (181+ mg/L) with this dark blue color.

Here is the complete chart:

mg/L To GPG Water Hardness Chart

mg/L of CaCO3: GPG (Grains Per Gallon):
1 mg/L of CaCO3 0.06 GPG
2 mg/L of CaCO3 0.12 GPG
3 mg/L of CaCO3 0.18 GPG
4 mg/L of CaCO3 0.23 GPG
5 mg/L of CaCO3 0.29 GPG
6 mg/L of CaCO3 0.35 GPG
7 mg/L of CaCO3 0.41 GPG
8 mg/L of CaCO3 0.47 GPG
9 mg/L of CaCO3 0.53 GPG
10 mg/L of CaCO3 0.58 GPG
15 mg/L of CaCO3 0.88 GPG
20 mg/L of CaCO3 1.17 GPG
25 mg/L of CaCO3 1.46 GPG
30 mg/L of CaCO3 1.75 GPG
35 mg/L of CaCO3 2.04 GPG
40 mg/L of CaCO3 2.34 GPG
45 mg/L of CaCO3 2.63 GPG
50 mg/L of CaCO3 2.92 GPG
55 mg/L of CaCO3 3.21 GPG
60 mg/L of CaCO3 3.51 GPG
65 mg/L of CaCO3 3.80 GPG
70 mg/L of CaCO3 4.09 GPG
75 mg/L of CaCO3 4.38 GPG
80 mg/L of CaCO3 4.67 GPG
85 mg/L of CaCO3 4.97 GPG
90 mg/L of CaCO3 5.26 GPG
95 mg/L of CaCO3 5.55 GPG
100 mg/L of CaCO3 5.84 GPG
110 mg/L of CaCO3 6.43 GPG
120 mg/L of CaCO3 7.01 GPG
130 mg/L of CaCO3 7.59 GPG
140 mg/L of CaCO3 8.18 GPG
150 mg/L of CaCO3 8.76 GPG
160 mg/L of CaCO3 9.35 GPG
170 mg/L of CaCO3 9.93 GPG
180 mg/L of CaCO3 10.52 GPG
190 mg/L of CaCO3 11.10 GPG
200 mg/L of CaCO3 11.68 GPG
210 mg/L of CaCO3 12.27 GPG
220 mg/L of CaCO3 12.85 GPG
230 mg/L of CaCO3 13.44 GPG
240 mg/L of CaCO3 14.02 GPG
250 mg/L of CaCO3 14.60 GPG
260 mg/L of CaCO3 15.19 GPG
270 mg/L of CaCO3 15.77 GPG
280 mg/L of CaCO3 16.36 GPG
290 mg/L of CaCO3 16.94 GPG
300 mg/L of CaCO3 17.53 GPG
310 mg/L of CaCO3 18.11 GPG
320 mg/L of CaCO3 18.69 GPG
330 mg/L of CaCO3 19.28 GPG
340 mg/L of CaCO3 19.86 GPG
350 mg/L of CaCO3 20.45 GPG
360 mg/L of CaCO3 21.03 GPG
370 mg/L of CaCO3 21.61 GPG
380 mg/L of CaCO3 22.20 GPG
390 mg/L of CaCO3 22.78 GPG
400 mg/L of CaCO3 23.37 GPG
410 mg/L of CaCO3 23.95 GPG
420 mg/L of CaCO3 24.54 GPG
430 mg/L of CaCO3 25.12 GPG
440 mg/L of CaCO3 25.70 GPG
450 mg/L of CaCO3 26.29 GPG
460 mg/L of CaCO3 26.87 GPG
470 mg/L of CaCO3 27.46 GPG
480 mg/L of CaCO3 28.04 GPG
490 mg/L of CaCO3 28.62 GPG
500 mg/L of CaCO3 29.21 GPG
550 mg/L of CaCO3 32.13 GPG
600 mg/L of CaCO3 35.05 GPG
650 mg/L of CaCO3 37.97 GPG
700 mg/L of CaCO3 40.89 GPG
750 mg/L of CaCO3 43.81 GPG
800 mg/L of CaCO3 46.73 GPG
850 mg/L of CaCO3 49.66 GPG
900 mg/L of CaCO3 52.58 GPG
950 mg/L of CaCO3 55.50 GPG
1000 mg/L of CaCO3 58.42 GPG

By checking this chart, you can see that:

  • “Soft” water has 0 to 3.55 GPG (corresponding to 0 to 60 mg/L of CaCO3).
  • “Moderately Hard” water has 3.66 to 7.05 GPG (corresponding to 61 to 120 mg/L of CaCO3).
  • “Hard” water has 7.06 to 10.56 GPG (corresponding to 121 to 180 mg/L of CaCO3).
  • “Very Hard” water contains more than 10.57 GPG (corresponding to over 181 mg/L of CaCO3).

With the conversion calculator above and this chart, you can now easily convert mg/L to GPG (of CaCO3). If you would need a bit of help, or have a suggestion to add, you can use the comment section below, maybe give us a number or two, and we can help you out.

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