PPM (Parts Per Million)

Parts Per Million (PPM) is a unit of measurement that expresses the concentration of a dissolved substance in a solution. In the context of plant nutrition, 1 PPM is equivalent to 1 milligram of dissolved solids per litre of water.

PPM is derived from EC readings using a conversion factor that varies by meter manufacturer and regional convention:

• 500 scale (used in North America): PPM = EC (mS/cm) × 500
• 640 scale (used by Hanna instruments): PPM = EC (mS/cm) × 640
• 700 scale (used in Europe and Australia): PPM = EC (mS/cm) × 700

Because of these different scales, PPM readings from different meters are not directly comparable. The EC reading is the universal standard, and it is generally recommended to work in EC to avoid confusion.

When comparing nutrient recommendations from different brands or regions, always clarify which PPM scale is being referenced.