Milligrams per milliliter, or mg/mL, is a measurement of a solution's concentration, the amount of one substance dissolved in a specific volume of a liquid. You can find the concentration of a solution by dividing the dissolved mass by the solution's volume.
What Are Solutions and Concentration?
A solution is composed of two parts. A solute, or substance that is dissolved, and a solvent, the liquid in which it is dissolved. Salt water is an example of a common solution. Solid salt, NaCl, is the solute, which is dissolved in a solvent of water.
The strength of a solution is measured in concentration. Concentration shows how much mass there is of the solute per volume of the solvent. Take a salt water solution of 5.7 milligrams per milliliter. This means there are 5.7 milligrams of salt in each milliliter of water.
Convert Your Mass to Milligrams
To find a concentration in milligrams per milliliter, you need to find the mass of your solute in milligrams. If your mass is already in milligrams, you can skip this step. You can quickly convert between metric mass units and milligrams. One gram, g, is equal to 1000 milligrams. One kilogram, kg, is equal to 1000 grams, or 1,000,000 milligrams. So if you have 7 grams of a substance, you can convert to milligrams by multiplying by 1,000, getting 7,000 milligrams.
You can also convert non-metric units to milligrams using different conversion formulas. Non-metric conversion formulas are a little more complicated. For instance, one ounce is equal to 28.35 grams, or 28,350 milligrams. So, to convert ounces to milligrams, you'd multiply the number of ounces by 28,350.
Convert Your Volume to Milliliters
As you did with mass, convert the volume of your solvent to milliliters. One liter, L, is equal to 1,000 milliliters, and one kiloliter is equal to 1,000 liters, or 1,000,000 milliliters. So, .75 kiloliters of water is the same as 750,000 milliliters.
You can also convert from non-metric units to milliliters. For instance, one cubic inch is equal to 16.4 milliliters. So, if you have 12 cubic inches of a solvent, you can convert it to milliliters by multiplying it by 16.4:
12 cubic inches x 16.4 milliliters/cubic inch = 196.8 milliliters
So, you have 196.8 milliliters of your solvent.
Divide Mass by Volume
You now have the mass of the solute and the volume of the solvent. To find the concentration, divide the mass in milligrams by the volume in milliliters.
Say you have a solution where 5 grams of sugar are dissolved in 300 milliliters of water. First, convert the mass of the sugar to milligrams. One gram is 1,000 milligrams, so 5 grams is 5,000 milligrams of sugar. Your volume is already in milliliters, so you can divide the mass of sugar by the volume of water to find the concentration:
5,000 milligrams / 300 milliliters = 16.67 milligrams/milliliter
So, the concentration of your solution is 16.67 milligrams per milliliter, which means there are 16.67 milligrams of sugar dissolved in each milliliter of water.