Convert between ppm, mg/L, ppb, percent, µg/L, g/L, and molarity. Includes solution density correction and EPA/WHO water quality reference.
Parts per million (ppm) and milligrams per liter (mg/L) are the two most common ways to express small concentrations in water treatment, environmental science, chemistry, and food analysis. While they are numerically equal for pure water (density 1.0 g/mL), this equivalence breaks down for seawater, concentrated solutions, acids, or any liquid with a density other than water.
This converter handles eight concentration units — ppm, mg/L, ppb, ppt (parts per trillion), percent, µg/L, g/L, and molarity — with a density correction factor so you get accurate results for any solution, not just water. It also calculates total dissolved mass for a given solution volume and provides EPA and WHO drinking water limits for quick reference.
Whether you're testing pool chlorine levels, analyzing wastewater discharge, checking drinking water compliance, or preparing laboratory solutions, this tool covers the full range of concentration conversions with the precision you need. Check the example with realistic values before reporting.
ppm and mg/L look interchangeable in water, but they are not the same thing once density changes. This page keeps density, molarity, and total dissolved mass in the same workflow so lab, water-treatment, and compliance calculations stay consistent. It is particularly useful when a limit is written in mg/L but the source data or instrument output is in ppm.
mg/L = ppm × density (g/mL) ppm = mg/L ÷ density ppb = ppm × 1,000 ppt = ppm × 1,000,000 % = ppm ÷ 10,000 µg/L = mg/L × 1,000 mol/L = (mg/L) ÷ (molar mass × 1,000)
Result: 0.015 ppm = 0.015 mg/L
15 ppb ÷ 1,000 = 0.015 ppm. At density 1.0, 0.015 ppm = 0.015 mg/L. This is the EPA action level for lead in drinking water.
Concentration is expressed as a ratio — the amount of solute relative to the total solution. The units differ in scale and in whether they are mass/mass, mass/volume, or amount/volume ratios. Understanding which ratio each unit represents prevents costly errors in dosing, compliance reporting, and research.
| Solution | Density (g/mL) | 100 ppm = ? mg/L | |---|---|---| | Pure water | 1.000 | 100.0 | | Seawater | 1.025 | 102.5 | | 10% NaCl brine | 1.071 | 107.1 | | Concentrated H₂SO₄ | 1.840 | 184.0 | | Ethanol | 0.789 | 78.9 |
For brines, acids, and organic solvents, using the wrong unit without density correction can introduce 5–80% error.
Environmental science uses ppb and ppt for trace pollutants (PFAS, heavy metals). Water treatment uses mg/L for chlorine, turbidity, and total dissolved solids. Chemistry labs use molarity for precise stoichiometric work. Agriculture uses ppm for soil nutrient concentrations. Food science uses ppm for flavorings and preservatives.
Only when the solution density is exactly 1.0 g/mL (pure water at 4 °C). For most dilute aqueous solutions, the difference is negligible, but for seawater, brines, or acids, they differ significantly.
ppm is a mass-to-mass ratio (mg/kg), while mg/L is mass-to-volume. Converting between them requires knowing how many kg are in a liter — that's the density.
Parts per billion. 1 ppb = 0.001 ppm = 1 µg/L (in water). EPA drinking water limits for heavy metals are often given in ppb or µg/L.
First convert ppm to mg/L using density, then divide by the molar mass in g/mol and convert mg to g. That gives you a concentration in moles per liter that matches the chemistry literature.
The EPA maximum contaminant level for chlorine residual is 4 mg/L (4 ppm). Municipal water typically contains 0.2–2 ppm.
Yes, ppm is exactly 1 mg per 1 kg (= 1 mg per 1,000,000 mg). For solids, ppm always means mg/kg.