PPM = (amount of solute ÷ total amount of solution) × 1,000,000
For mass-based calculations: PPM = (mass of solute in mg ÷ mass of solution in kg)
For dilute aqueous solutions: PPM ≈ (mg of solute ÷ L of solution)
Convert units first if needed
Use the same units consistently before calculating
Example: 5 mg solute in 1 L water = 5 ppm