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Convert between EC, PPM-500, PPM-700, and TDS-442 scales instantly
Enter Value
Input Unit
EC
1.20
mS/cm
Bluelab, Hanna, Apera
PPM (500 scale)
600
ppm
Hanna, Milwaukee
PPM (700 scale)
840
ppm
Truncheon, Bluelab
TDS (442 scale)
530
ppm
Some TDS meters
EC Target Ranges by Growth Stage
Not sure which scale your meter uses?
Hanna: Usually 500 scale (check settings menu)
Bluelab: Can be set to EC, 500, or 700 scale
Truncheon: 700 scale (printed on the stick)
Milwaukee: Check manual, usually 500 scale
When in doubt, switch your meter to EC mode for the most reliable readings.
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Create Free Account →Electrical Conductivity (EC) measures how well your nutrient solution conducts electricity, which directly correlates with the total dissolved salts (nutrients) in the water. Pure water has an EC of 0, and as you add nutrients, the EC rises. It's measured in milliSiemens per centimeter (mS/cm) and is the most reliable way to gauge nutrient strength.
EC doesn't tell you which specific nutrients are present — only the total concentration. To know individual nutrient levels, you'd need a lab test. But for day-to-day growing, EC is the standard tool for mixing consistent nutrient solutions and monitoring root zone conditions.
PPM (Parts Per Million) is not a direct measurement — it's calculated from EC using a conversion factor. The problem is that different meter manufacturers use different conversion factors. The three common scales are:
This means the same nutrient solution reads 600 PPM on one meter and 840 PPM on another. When someone tells you to "mix to 800 PPM," you need to know which scale they mean. EC avoids this confusion entirely — 1.2 EC is 1.2 EC on every meter.
The most common mistake in growing is following a nutrient chart that uses 700-scale PPM readings with a meter that reads 500-scale (or vice versa). This can lead to over- or under-feeding by 40%. To avoid this: always ask what scale a PPM recommendation uses, or better yet, convert everything to EC. Most nutrient manufacturers now include EC values alongside PPM in their feeding charts.
What is EC in hydroponics?
EC measures the total dissolved salts in your nutrient solution. Higher EC means more nutrients. It's the most reliable way to monitor nutrient strength.
Why is EC more reliable than PPM?
EC is a direct measurement, while PPM depends on a conversion factor that varies between meters. The same solution reads different PPM on different meters.
What is the difference between PPM 500 and PPM 700?
They use different conversion factors. A 1.0 EC solution reads 500 PPM on a 500-scale meter and 700 PPM on a 700-scale meter.
How do I know which PPM scale my meter uses?
Check your meter's manual or settings. Hanna = 500, Truncheon = 700, Bluelab = configurable. When in doubt, use EC.
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