PPM to Molarity Calculator

The ppm to molarity calculator (parts per million) will convert ppm to molarity for any element or molecule dissolved in water.

The conversion from ppm to molarity, or back from molarity to ppm, is quite simple. Just read on below to learn more!

Both ppm (parts per million) and molarity are measures of concentration. Did you know that ppm is used in different ways depending on the context? When dealing with dilute solutions, 1 ppm can be approximated as $1\ \text{mg}$ of substance per liter of water, or $1\ \text{mg}/\text{L}$.

On the other hand, molarity is molar concentration, meaning that it tells you how many moles of molecules are in one L of solution. The symbol M is used to denote the unit of molarity. So, for example, 1 M means there is 1 mole of substance in one liter of solution.

Many concentration calculations use the mole units because we're dealing with a great number of molecules. There are $6.0221409 \times 10^{23}$ molecules or particles in one mole.

If you want to know more about ppm and molarity, visit our dedicated calculators, the ppm calculator and the molarity calculator.

Some situations where you may need to convert ppm to molarity include:

• Measurements of drinking water quality;
• Maintenance of chemical levels in aquariums;
• Mixing fertilizer solutions for horticulture; and
• Producing chemical solutions.

You will need a different ppm calculation if you are using it in other contexts, such as:

• ppm of a nutrient in soil (which uses $\text{mg}$ nutrient per $\text{kg}$ of soil); and
• ppm of pollutants in air (which uses $\text{μL}$ of pollutant per $\text{L}$ of air).

So, what is ppm? And how can something called "parts per million" be represented by $\text{mg}/\text{L}$? Parts per million indicates the number of "parts" of something in a million "parts" of something else. The "part" can be any unit, but when mixing solutions, ppm will usually represent weight units. In this context, ppm tells you how many grams of a solute are for each million grams of solution.

When dealing with a diluted solution in water at room temperature, we can approximate the mass of the solvent to the total mass of the solution and assume the density of water to be $1\ \text{g}/\text{mL}$. Therefore, we can rewrite the relationship as follows:

Then we divide $\text{mL}$ by $1000$ to convert mL to L: the easiest volume conversion!

By dividing both units by $1000$, the ratio becomes:

Therefore, you can say that $1\ \text{mg}$ in $1\ \text{L}$ water is the same as $1\ \text{mg}$ in $1,000,000\ \text{mg}$ water, or 1 part per million (assuming both room temperature and an atmospheric pressure of $1\ \text{atm}$).

If your solvent is not water, you should adjust the solvent's density in the calculator.

To convert ppm to molarity, or molarity to ppm, you only need to know one thing: the molar mass of the dissolved element or molecule.

If you take molarity (with units $\text{mol}/\text{L}$) and multiply it by the molar mass (with units $\text{g}/\text{mol}$), you get $\text{g}/\text{L}$. Just multiply $\text{g}/\text{L}$ by $1000$ to convert $\text{g}$ to $\text{mg}$, and you have ppm (in $\text{mg}/\text{L}$ of water).

This ppm to molarity formula for dilute solutions is:

The average salt content in seawater is equivalent to $0.599\ \text{M}$ $\text{NaCl}$ (although sea salts are not entirely made up of $\text{NaCl}$). If the EPA recommends that drinking water should not exceed $20\ \text{mg}/\text{L}$ (or $20\ \text{ppm}$), how many times more salty is seawater compared to drinking water?

To find out, let's convert $0.599\ \text{M}$ $\text{NaCl}$ into $\text{ppm}$. We need to know the molar mass of $\text{NaCl}$, which is $58.44\ \text{g}/\text{mol}$. Multiply the molarity by molar mass to get $\text{g}/\text{L}$:

Next, multiply by $1000$ to get $\text{mg}/\text{L}$:

Finally, divide the salt concentration of sea water by the drinking water guideline to find their ratio:

The significant figures we calculated are too many: reduce them to 3. Then, we can say that seawater is approximately $1750$ times saltier than drinking water!

You have a stock solution of 1 molar $\text{NaOH}$. How do you go about creating a $1\ \text{L}$ solution of $200\ \text{ppm}$ $\text{NaOH}$? $\text{NaOH}$ has a molar mass of $39.997\ \text{g}/\text{mol}$.

1. Convert $200\ \text{ppm}$ to molarity.

Let's first assume $200\ \text{ppm} = 200\ \text{mg}/\text{L}$. Then, divide the result by $1000$ to get $\text{g}/\text{L}$:

$200\ \text{mg}/\text{L}$ divided by $1000\ \text{mg}/\text{g}$ is equal to $0.2\ \text{g}/\text{L}$.

Next, divide $0.2\ \text{g}/\text{L}$ by the molar mass of $\text{NaOH}$ to get the molarity:

$0.2\ \text{g}/\text{L}$ divided by $39.997\ \text{g}/\text{mol}$ is equal to $0.005\ \text{mol}/\text{L}$.

2. Calculate the dilution recipe.

From step 1, we know the target molarity is $0.005\ \text{mol}/\text{L}$. To calculate the dilution, we use the dilution equation:

where:

• $m_1$ — The concentration of stock solution;
• $m_2$ — The concentration of diluted solution;
• $V_1$ — The volume of stock solution; and
• $V_2$ — The volume of diluted solution.

We can fill in the numbers for all the variables except for the volume of stock solution:

By rearranging the equation, we will find the volume of stock solution required:

Therefore, we need to dilute $0.005\ \text{L}$ (or $5\ \text{mL}$) of stock solution to a final volume of $1\ \text{L}$ to get a $200\ \text{ppm}$ $\text{NaOH}$ solution.

You can check Step 1 with this ppm to molarity calculator and check Step 2 with the solution dilution calculator!