mg/L To mEq/L Calculator: Convert mg/L To mEq/L (+ Chart)

When you are dealing with water solutions, you will sometimes have to convert concentrations from mg/L to mEq/L (milligrams per Liter to milliEquivalents per Liter). This is not exactly the easiest conversion, so we will help you with an online mg/L to mEq/L calculator.

Below the calculator, we will look at a formula for this conversion and a few examples. Since the mg/L to mEq/L conversion depends on atomic/molecular weight and valence (ion charge), we created 2 conversion charts (1st for potassium (K+), 2nd for calcium (Ca2+)).

By the way, you can find a lot of common atomic/molecular weights and valences (K+, Na+, Li+, Ca2+, Mg2+, Fe3+, etc.) you will need to use the calculator in the appendix at the bottom of this article. Here’s the calculator:


Alright, let’s make one conversion to illustrate how to use this calculator:

Say you have a 100 mg/L solution of NaOH and would like to know how many mEq/L that is. You insert ‘100’ in the mg/L input field, the molecular mass of NaOH is 40 g/mol, so you insert ’40’ in the 2nd input field, and we know Na1+ in NaOH has +1 charge, and thus we slide the valence/charge slider to ‘1’. Here is the result we get (screenshot):

converting mg l to meq l with an online calculator

We can see right away that 100 mg/L NaOH solution is equal to 2.5 mEq/L solution.

Let’s look at how the mg/L to mEq/L calculation works:

mg/L To mEq/L Formula

Namely, we use both mg/L and mEq/L as units of concentration in water solutions. Here are the short definitions:

  • mg/L stands for milligrams per liter. 1 mg/L means that we dissolved 1 mg of a chemical in 1 liter of water.
  • mEq/L stands for milliequivalents per liter. This is a bit of an old-school unit of concentration that we still use in chemistry, biology, and so on. 1 mEq/L is the amount of chemical substance we need to reach with 1 millimole (mmol) of another substance, usually hydrogen ions.

The conversion between mg/L and mEq/L depends on atomic/molecular mass (usually an atomic mass of ions such as potassium, sodium, calcium, etc.) and the iron charge (+1, +2, +3, -1, -2, -3, etc.). Here is the full mg/L to mEq/L formula:

mEq/L = (mg/L × Valence or Ion Charge) / Atomic or Molecular Weight

We see that we need to multiply mg/L concentration by ion valence/charge, and divide this product by atomic/molecular weight of the atom/molecule, to get the equivalent mEq/L concentration.

Quick Example: How many mEq/L is 150 mg/L solution of magnesium (Mg2+)? We know that we have a 150 mg/L solution; from the appendix below, we see that the atomic mass of magnesium is 24.3 g/mol, and it has a +2 valence or charge. We insert all these numbers in the equation like this:

mEq/L (150 mg/L Mg2+) = (150 mg/L × 2) / 24.3 g/mol = 12.35 mEq/L

We see that 150 mg/L of magnesium ions is equivalent to 12.35 mEq/L.

This is just one example. We converted mg/L to mEq/L for potassium ions and calcium ions to create these 2 helpful conversion charts:

Potassium mg/L To mEq/L Conversion Chart

Potassium has an atomic weight of 39.1 g/mol and +1 valence. Here are the conversions:

Potassium mg/L (K+): Potassium mEq/L:
0.01 mg/L K+ 0.00026 mEq/L
0.1 mg/L K+ 0.0026 mEq/L
1 mg/L K+ 0.026 mEq/L
2 mg/L K+ 0.051 mEq/L
3 mg/L K+ 0.077 mEq/L
4 mg/L K+ 0.102 mEq/L
5 mg/L K+ 0.128 mEq/L
10 mg/L K+ 0.256 mEq/L
20 mg/L K+ 0.512 mEq/L
30 mg/L K+ 0.767 mEq/L
40 mg/L K+ 1.023 mEq/L
50 mg/L K+ 1.279 mEq/L
60 mg/L K+ 1.535 mEq/L
70 mg/L K+ 1.790 mEq/L
80 mg/L K+ 2.046 mEq/L
90 mg/L K+ 2.302 mEq/L
100 mg/L K+ 2.558 mEq/L
150 mg/L K+ 4.049 mEq/L
200 mg/L K+ 5.399 mEq/L
250 mg/L K+ 6.749 mEq/L
300 mg/L K+ 8.098 mEq/L
350 mg/L K+ 9.448 mEq/L
400 mg/L K+ 10.798 mEq/L
450 mg/L K+ 12.147 mEq/L
500 mg/L K+ 13.497 mEq/L

Calcium mg/L To mEq/L Conversion Chart

Calcium has an atomic weight of 40.08 g/mol and +2 valence. Here are the conversions:

Calcium mg/L (Ca2+): Calcium mEq/L:
0.01 mg/L Ca2+ 0.0005 mEq/L
0.1 mg/L Ca2+ 0.005 mEq/L
1 mg/L Ca2+ 0.050 mEq/L
2 mg/L Ca2+ 0.100 mEq/L
3 mg/L Ca2+ 0.150 mEq/L
4 mg/L Ca2+ 0.200 mEq/L
5 mg/L Ca2+ 0.250 mEq/L
10 mg/L Ca2+ 0.499 mEq/L
20 mg/L Ca2+ 0.998 mEq/L
30 mg/L Ca2+ 1.497 mEq/L
40 mg/L Ca2+ 1.996 mEq/L
50 mg/L Ca2+ 2.495 mEq/L
60 mg/L Ca2+ 2.994 mEq/L
70 mg/L Ca2+ 3.493 mEq/L
80 mg/L Ca2+ 3.992 mEq/L
90 mg/L Ca2+ 4.491 mEq/L
100 mg/L Ca2+ 4.990 mEq/L
150 mg/L Ca2+ 7.485 mEq/L
200 mg/L Ca2+ 9.980 mEq/L
250 mg/L Ca2+ 12.475 mEq/L
300 mg/L Ca2+ 14.970 mEq/L
350 mg/L Ca2+ 17.465 mEq/L
400 mg/L Ca2+ 19.960 mEq/L
450 mg/L Ca2+ 22.455 mEq/L
500 mg/L Ca2+ 24.950 mEq/L

With the formula, these charts, and especially the online calculator, you are now able to convert mg/L to mEq/L for any ion or molecule. If you need a bit of help, you can always use the comment section below, tells us what you’re trying to convert, and we can help you out.

Here is the aforementioned appendix for ion weights and valences:

Appendix: Atomic Weight Table With Ion Valence

Main Atom: Atomic Weight: Valence (Charge):
K (Potassium) 39.1 g/mol 1
Na (Sodium) 23.0 g/mol 1
Li (Lithium) 6.94 g/mol 1
Ca (Calcium) 40.08 g/mol 2
Mg (Magnesium) 24.3 g/mol 2
Fe (Iron 3-valent): 55.85 g/mol 3
Cu (Copper 2-valent): 63.55 g/mol 2
Zn (zinc 2-valent): 65.38 g/mol 2
F (Fluoride): 19.0 g/mol 1
Cl (Chloride): 25.45 g/mol 1
Br (Bromide): 79.9 g/mol 1
O (Oxide): 16.0 g/mol 2
S (Sulfur): 32.07 g/mol 2
P (Phosphor): 30.97 g/mol 3
N (Nitrogen): 16.0 g/mol 3
C (Carbon): 12.0 g/mol 4

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