Concentration, ppm and ppb converter

Why density matters

Here ppm and ppb mean the mass of solute divided by total solution mass. By contrast, mg/L describes mass per litre of solution. Density connects those definitions. At 1000 kg/m³, 10 ppm equals 10 mg/L numerically. At 800 kg/m³, the same 10 ppm equals only 8 mg/L.

Select the units

The mass fraction field accepts percent, ppm or ppb. Mass concentration can be entered in mg/L, g/L or kg/m³. To convert to molarity, also provide the solute molar mass. Gas concentrations by volume and liquid volume percentages use different definitions and cannot be entered as mass fractions. The calculator does not check solubility or chemical compatibility.

Convert by hand using density

For an example solution, take mass fraction 25 ppm, density 1200 kg/m³ and example molar mass 60 g/mol. One litre of solution has mass 1.2 kg, so solute concentration is 25 mg/kg × 1.2 kg/L = 30 mg/L. This equals 0.030 g/L. Molarity is 0.030 / 60 = 0.0005 mol/L. The molar mass and density are not tabulated properties of a specified substance.

In reverse, dividing 30 mg/L by density 1.2 kg/L returns 25 mg/kg, or 25 ppm. This check shows that mass fraction and concentration based on volume have different denominators. Do not assume that every ppm value equals mg/L by treating every solution as water.

Read the measurement report's definition of ppm first. The same abbreviation can mean volume fraction or mole fraction in gases. Such values do not belong in this tool's mass fraction input. Density must refer to the whole solution, not pure solute. Match molar mass to the chemical species reported by the analysis. Combining an ion concentration with the molar mass of the entire salt changes the conversion.

Frequently asked questions

How do you convert mg/L to ppm?

For example, dividing mass concentration by solution density gives 25 ppm for 20 mg/L and 800 kg/m³. In water at 1000 kg/m³ the numbers of mg/L and ppm are equal, and they differ when the density differs. This is a mass fraction, not a volume fraction.

Calculate with these values