EC / PPM Converter
Convert between EC and PPM, and see how the same reading looks on each of the three common meter scales.
Result: 700 ppm on the 500 scale
Same reading on other scales: 640 scale: 896 ppm, 700 scale: 980 ppm. Mixing these up is a common, real cause of over- or under-fertilizing — always confirm which scale your own meter uses.
Use the result with the nutrient dosing calculator to account for your source water’s own baseline EC.
Frequently asked questions
- Why do EC and PPM readings from different meters disagree?
- EC (electrical conductivity, in mS/cm) is what the sensor actually measures. PPM is a derived number obtained by multiplying EC by a conversion factor that varies by meter brand: commonly 500, 640 (sometimes shown as 650), or 700. The same 1.4 mS/cm reading is 700 ppm on a 500-scale meter but 980 ppm on a 700-scale meter — a real, well-documented source of nutrient dosing errors when a feeding chart written for one scale is read against a meter using another.
- Which scale does my meter use?
- It depends on the brand and model — this tool doesn't detect it for you, and manufacturers' own "chemical standard" names for these scales (NaCl, KCl, 442) are used inconsistently, so don't rely on a label alone. HM Digital meters and Hanna Instruments' DiST pocket testers are datasheet-confirmed at the 500 scale (factor 0.5); some meters, including certain Bluelab models, also display a 700-scale reading. The 640 scale is a generic default some references use when the calibration standard isn't stated. Check your meter's manual for its actual numeric conversion factor.
- Should I just use EC instead of PPM?
- Many experienced growers do exactly that, since EC has no scale ambiguity — it's the same physical measurement everywhere. If your nutrient brand's feeding chart is published in ppm, convert it to EC once using your meter's known scale, then track EC going forward.