What does 1 mg/L equal in terms of parts per million?

One milligram per liter (mg/L) is equivalent to one part per million (ppm) in terms of concentration measurement. This equivalence arises because both units are used to express the concentration of a substance in a solution, particularly in water quality testing. Specifically, 1 mg/L indicates that there is one milligram of a solute present in one liter of solution. Since one liter of water is approximately equal to one million milligrams, the ratio of solute (in mg) to solution (in L) directly translates to parts per million. Therefore, when a concentration is specified as 1 mg/L, it captures the same meaning as saying there is one part of that substance in one million parts of water, confirming that 1 mg/L is indeed equal to 1 ppm.