EC ↔ ppm / TDS converter
Meters report either EC or a “ppm” that is just EC scaled by a standard. There is no single true conversion: it depends on the meter's scale, so always store which scale a ppm value came from.
Input
Result
Converted on the selected meter scale
1000 ppm on a 500-scale meter is not 1000 ppm on a 700-scale meter. When you share or store a ppm number, record the scale alongside it: otherwise the value is ambiguous by up to 40%.
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How do you convert EC to ppm in hydroponics?
Multiply EC (mS/cm) by your meter's conversion factor: 500 for the 500 scale, 640 for 640, or 700 for the Australian/NaCl scale. A reading of 1.8 mS/cm is about 900 ppm on the 500 scale but 1,260 ppm on the 700 scale, so always check which scale your meter uses before comparing readings. Use the calculator above to convert either direction with temperature correction.