Parts Per Million (ppm) Calculator

Parts per million (ppm) is one of the most widely used concentration units in science and environmental monitoring. It expresses the amount of one substance dissolved or dispersed in another as a ratio of one to one million by mass or by volume. This calculator covers two common tasks: working out the ppm of a solution from the mass of dissolved solute and the total mass of the solution, and converting a known ppm value into equivalent units including milligrams per litre (mg/L), milligrams per kilogram (mg/kg), parts per billion (ppb) and percentage by mass. For dilute aqueous solutions, 1 ppm is very close to 1 mg/L, because the density of water is approximately 1 kilogram per litre and the mass of the dissolved substance is negligibly small compared with the water. This is why water quality results in New Zealand and internationally are often reported interchangeably in ppm and mg/L. In soil science and agricultural contexts, ppm is typically expressed as mg/kg, meaning milligrams of substance per kilogram of dry soil or sample. The New Zealand Drinking Water Standards (NZDWS) published by the Ministry of Health set maximum acceptable values for common contaminants in mg/L (ppm), and these are the reference for public water supply compliance in New Zealand under the Water Services Act 2021. This calculator is intended for educational and planning purposes. Always refer to the relevant New Zealand standard or laboratory report for regulatory compliance.

ppm = (solute mg / solution g) x 1000 for mass/mass, or solute mg / solution mL for dilute aqueous solutions. For regulatory water quality limits refer to the NZ Drinking Water Standards.