PPM and EC Converter
The same nutrient solution reads three different PPM numbers depending on the scale. Enter an EC value or a PPM reading and see it translated across the 500, 640, and 700 scales, so charts and meters finally agree.
Some meters show µS/cm — 1800 µS/cm is 1.8 mS/cm.
Formula & how it works
Each scale is a simple multiplier on EC in mS/cm: ppm = EC × factor, where the factor is 500, 640, or 700. Going the other way, EC = ppm ÷ factor.
Worked example
An EC of 1.8 mS/cm is 900 ppm on the 500 scale, 1,152 on the 640 scale, and 1,260 on the 700 scale. So a chart calling for "900 ppm" and a European meter showing 1,260 can describe exactly the same solution — the difference is convention, not strength.
Reading nutrient strength
EC is the real measurement
Meters measure electrical conductivity, which rises with dissolved salts. PPM is a derived figure obtained by multiplying EC by a chosen factor, so quoting EC removes all ambiguity. When you record grow logs, noting EC makes them portable between meters and regions.
Know your meter's scale
Most US meters default to the 500 scale, while the 700 scale dominates in Europe and Australia and 640 appears on some Eutech instruments. That is a 40% spread between 500 and 700 for the same solution — enough to seriously overfeed or starve a crop if a chart is followed on the wrong scale.
Conductivity does not identify nutrients
EC tells you how much dissolved salt is present, not which salts. A reservoir can drift toward the right EC while its balance of elements shifts as plants take up some faster than others. That is why periodic reservoir changes matter, rather than endlessly topping up to a target number.