What is ppm?  Parts per million (ppm) is the measurement of dissolved salts in solution referred to as Total Dissolved Solids (TDS).  Plant nutrients/fertilizers are generally essential solid salts that have been dissolved into water/solution - this allows nutrients to be absorbed ionically through the roots of plants.  Typically, a ppm meter will take an EC reading of a solution in μS/cm2 (microsiemens) and then convert and display a reading in ppm.  The most confusing part about using a parts per million meter is the fact that manufacturers of the meters use 3 different conversion factors from EC to achieve a ppm readout, depending on which country you live in - 0.50, 0.64 and 0.70.  The use of ppm when measuring the strength/concentration of nutrients in solution is not optimal, a bit cumbersome and prone to error or confusion. 

What is EC?  Electrical Conductivity (EC) is a measurement of the ability of something to conduct electricity.  In horticulture, EC is used to determine nutrient strength because the dissolved solids (elements) essential for plant life, generally display the ability to conduct electricity in solution.  By measuring the electrical conductivity (EC), rather than parts per million (ppm), you will see a more accurate measurement of nutrient strength.  The units chosen to measure EC commonly are μS/cm2 (microsiemens) abbreviated as simply μS and also mS/cm2 (millisiemens) abbreviated as simply mS.  Typically, laboratories worldwide use EC meters over ppm meters for accuracy purposes. 

How do I measure ppm and EC?  Please see Usage Instructions and Tips

When faced with measuring nutrient strength, many entry-level growers may be confused by the radical terminology being tossed around.  EC, ppm, TDS - what do these acronyms mean and why is it important to plants?  The primary reason nutrient strength measurements should be taken in EC instead of ppm is, that depending on your geographical location, and particular meter used, your ppm measurement may differ greatly from that of the feed chart from your favorite nutrient regime, such as Dutch Master’s new Commercial Edition.  This is due to the fact that various meter manufacturers choose to calculate ppm using differing ratios.  To derive the ppm value on these meters, EC is first measured, then multiplied by a particular ratio to yield a value for ppm.  Much of the U.S. will experience a 0.50 conversion ratio, whereas many other parts of the world utilize a 0.64 and even 0.70 conversion ratio.  As you can see, this lack of standardization with regard to EC to ppm calculations/conversions can lead to much confusion and many mix-ups.  Dutch Master always prefers to use EC as a measurement of nutrient strength to avoid communication errors with clients, however, if we do refer to ppm’s, we will use the gold standard of conversion factors - 0.50. 

What is the perfect EC?  The short answer - there is no such thing!  Each plant and or strain will have greatly varying nutrient requirements depending on many variables.  Early in a plant’s life cycle, less nutritive enhancement will be required and alternately, if your nutrient solution is too concentrated/strong, you run the risk of leaf tissue burn and necrosis.  Young plants, in particular, are especially susceptible to this and care should be taken to keep the EC adequately low.  As plants mature, their nutrient requirements begin to increase substantially and with this, an increase in EC will be required.  If plants are not given a high enough EC, growth will suffer and nutrient deficiencies may begin to appear.  Of course, certain strains will have a broader range of tolerable EC levels while others have a very narrow window of tolerable EC levels.  Another key factor to consider is media type, as various grow systems will have differing EC requirements.  For example, water culture techniques (DWC, NFT and aeroponics) in which the plants roots are in direct contact with nutrient solution, require a less concentrated nutrient solution as compared to a media that “buffers” and requires a higher nutrient concentration or EC.  Finding the sweet spot for a particular growth phase can be hard work - but with the Dutch Master Commercial Edition Feed Charts, you will be better equipped to know the appropriate nutrient EC levels for your plants throughout their entire life cycle.  Remember to watch your plants leaves for over (burnt leaf tips) or under (light rather than dark green) feeding signs and always make small changes to your nutrient strengths rather than large changes as it will lessen the chance of shocking / damaging your plants. 


  • ppm stands for parts per million & is the most common domestically used unit when measuring TDS. 
  • EC stands for electrical conductivity, which is a measurement of the ability of something to conduct electricity.  In horticulture, EC is the most accurate way to measure nutrient concentration in solution.  Typically, μS/cm2 (microsiemens) is the standard measurement of EC for laboratories. 
  • TDS stands for total dissolved solids and is a measurement of dissolved salts in solution. 
  • CF stands for concentration factor and is rarely used professionally in measuring nutrients. 
  • If ppm is favored, knowing your particular meters’ conversion ratio is crucial to successful crops.  Find out from your ppm meter manufacturer what particular ratio is used to determine what the true EC of your solutions may be.  Remember, 500ppm to you may be 640ppm or 700ppm to others! 
  • Water culture techniques will require slightly less concentrated nutrient solution since the roots are in direct contact with the solution, compared to other media’s including soil and soilless. 
Conversion Table