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 is full of impurities, in our case, 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; you can 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 is referring to when using the ppm setting?

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

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

What Bluelab setting should you use?

Listen, dont make it hard on yourself, and use the EC setting, the international scale, for conductivity. What you see is what you’ll get with an EC readout. 

If you must grow using ppm, you will need to know the following;

  • What ppm scale is the feeding schedule referring to? Find out before you add food or make a mix!
  • What ppm scale is your meter using? Ensure it matches the feeding schedule or book.
  • What ppm scale is the nutrient formula referring to? Match your meter to this!

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,


cartier crops

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