EC & PPM Converter

The same reading on each scale. Read across from the EC on the meter, or find the ppm a recipe gives in the column for its scale.

Conductivity rises with temperature by roughly 2% per °C, so the same solution reads higher when warm. Meters quote everything at 25 °C. A meter with ATC (automatic temperature compensation) has already applied this correction. Without it, correct here.

PPM Meter Basics

A handheld meter cannot weigh dissolved solids. It measures electrical conductivity, which is how well the water carries a current. That goes up as you dissolve more salt in it.

"ppm" is that conductivity multiplied by a constant the manufacturer picked, based on which reference salt they assume your solution is made of. Potassium chloride conducts better than sodium chloride, so the same EC implies a different mass depending on the assumption:

• 500 scale (sometimes "TDS NaCl", common on US meters): ppm = EC × 500
• 640 scale: ppm = EC × 640. This is the factor Bizon's own Water Quality tool uses.
• 700 scale (sometimes "TDS KCl", common on European and Australian meters): ppm = EC × 700

So 2.0 mS/cm is 1000, 1280 or 1400 ppm, depending on the scale. This is why a recipe that says "feed at 800 ppm" is ambiguous and one that says "feed at 1.6 mS/cm" is not.

EC is the actual measurement. If a recipe requires ppm, find out your meter's scale (it's in the manual, and often printed near the display) and write it down next to every number you record. EC can't tell you which salts are in the water. A solution short on calcium and high in sodium can read exactly the same EC as a perfectly balanced one.