How To Read An EC Conversion Chart

EC Conversion Chart Explained

Before understanding the EC conversion chart, you might ask this question. EC, CF, ppm500, ppm700, TDS… What’s the difference?

Which should you use, EC vs. PPM? Pure water will not conduct electricity. Water usually conducts electricity because it contains impurities like electrically charged nutrient ions. 

The two black dots on the Bluelab conductivity probes are called electrodes. When these get placed in a solution, an electrical current passes from one electrode through the water to the other electrode and counts the number of electrically charged ions present. The reading is then presented as an Electrical Conductivity (EC) reading or Conductivity Factor (CF) reading. EC and CF are measures of electrically charged nutrient ions in a solution. 

A mass concentration of 2mg/kg – 2 parts per million – 2ppm – 2 x 10-6. PPM measures parts per million. Known as dimensionless quantities, they are pure numbers with no associated units of measurement.

Many different scales get used for various industries worldwide and many various reasons! Did you even know there are more than two scales? Widely used ppm scales in hydroponics are the ppm500 scale, ppm650 scale, and ppm700 scale.

What’s the difference between ppm500 and ppm700 scales? EC Conversion Chart

  •  It is based on the ppm 700 scale, measuring a solution’s KCl or potassium chloride content.
  • The 500 ppm measures the NaCl or sodium chloride content of a solution.
  • The ppm 500 scale is also TDS – total dissolved solids.

With chemical analysis, you can determine the proper ppm solution and not measure ppm with an EC reader. You’ll see both settings on the Bluelab as a conversion guide only. 

Here’s the conversion from EC to ppm:

  • ppm500 = EC x 500
  • ppm700 = EC x 700

Examples of how this works, using a conductivity reading of 2.4EC:

  • ppm500 scale: 2.4EC x 500 = 1200ppm [500 scale]
    • (or 1200ppm / 500 = 2.4EC)
  • ppm700 scale: 2.4EC x 700 = 1680ppm [700 scale]
    • (or 1680ppm / 700 = 2.4EC)

If your nutrient line says you should grow your crop at 1100ppm – How do you know which scale the nutrient company refers to when using the ppm setting?

Matching the scale on your meter to the scale from the nutrient supplier is crucial. 

Ask Yourself This.

Is the scale on your ppm meter right for the job? If it’s US-made nutrients, it could be 650 or 500 scales. If the nutrients are made in the UK, it could be 700 scales. Australian-made nutrients, it could use the 700 scales!

ec conversion chart
courtesy of Bluelab

Which To Use EC or PPM?

Choosing between EC and PPM as your go-to metric often depends on your location and preference. In the United States, growers are more accustomed to PPM, while EC is more commonly used in Europe.

Regarding simplicity, EC is generally considered easier to read and understand, primarily because it is a standard unit of measurement worldwide. The EC value tells you the nutrient solution’s strength without worrying about different conversion factors or scales.

Although widely used, PPM can be a bit trickier because of the aforementioned scales. The 500 scale (Truncheon) is more common in the U.S. and is based on an older standard. Meanwhile, the 700 scale (Hanna) is based on a newer standard and is more accurate for most nutrient solutions used today.

It’s important to remember that your nutrient supplier will likely provide guidelines in both PPM and EC, so growers can use the scale they’re most comfortable with.

In conclusion, while EC might be easier to read, the choice between EC and PPM will depend on your familiarity with the system, location, and the recommendations provided by your nutrient solution manufacturer. Remember, the key is consistency in your measurements and adjustments for optimal plant health and yield.

EC Conversion Conclusion

Getting confused about EC, PPM, and TDS is average. Using a meter and the EC setting will eliminate your nutrient issues. Sure, if youre an organic grower, the soil feeds itself, but what if you run into a problem like nutrient depletion? You need to boost the soil. Your plants will thrive by measuring a proper dose of nutrients like SimPro formula at a specific EC and watering. Using the EC setting, indoor plants will grow faster, stronger, and bushier. Again, if you insist on using the PPM scale, check with the nutrient provider to ensure their schedule uses the 500 or 700 scales. 

Much Love,



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Cartier Crops has been breeding seeds since 1998. In 2018, he started helping dedicated cultivators in the cannabis industry. Through his content, Cartier shares advanced techniques, the latest research, and expert insights to support growers. With his guidance, 28,000 individuals have turned into successful plant-growing champions.

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