Hydroponic EC to PPM Converter
Convert between electrical conductivity (EC) and parts per million (PPM) for your nutrient solution. The result is shown on all three common PPM scales so you can match your meter.
How the conversion works
PPM is an estimate of dissolved solids worked out from EC with a fixed factor:
PPM = EC (mS/cm) × 500, 640 or 700 and EC = PPM ÷ 500, 640 or 700
Example: a solution at 1.8 mS/cm reads 1.8 × 500 = 900 ppm on the 500 scale, 1.8 × 640 = 1,152 ppm on the 640 scale and 1.8 × 700 = 1,260 ppm on the 700 scale. Going the other way, 800 ppm on the 500 scale is 800 ÷ 500 = 1.6 mS/cm.
Why there are three scales
The factor depends on which salt the meter is calibrated against, and brands differ: Hanna meters are commonly listed on the 500 scale, Eutech on 640 and Bluelab on 700, so check your manual. The 500 scale is based on a sodium chloride (NaCl) reference, the 700 scale on potassium chloride (KCl), and the 640 scale sits between them. None is "more correct" for nutrient water, which is a mix of many salts, so EC is the more reliable number to track. Pick the scale that matches your meter and your feeding chart and stay consistent.
New to this? Read the EC vs PPM guide. Once you have your target, work out how much nutrient to add with the hydroponic PPM calculator.
Values are estimates. Check your meter against a calibration solution regularly and follow your nutrient manufacturer's recommendations.
Frequently asked questions
Why does my meter show a different PPM than this converter?
PPM is not measured, it is calculated from EC. Meters use different conversion factors, so the same water can read 900, 1,152 or 1,260 ppm. Check which scale your meter uses (often printed in the manual or on the back) and pick it here.
Which PPM scale should I use?
Use the one your meter uses. If you do not know, the 500 scale (EC × 500) is the common default on many US-sold meters, 640 is used by some Milwaukee and Eutech meters, and 700 is used by Hanna and other brands. When you follow a feeding chart, make sure its ppm figures were written for the same scale as your meter.
What EC should I aim for?
It depends on the crop and growth stage. Lettuce and leafy herbs are often grown at roughly 1.0 to 1.8 mS/cm, while fruiting plants such as tomatoes usually run higher. Follow your nutrient maker's guidance for your crop.
Are mS/cm and dS/m the same?
Yes. 1 mS/cm equals 1 dS/m, and 1 mS/cm equals 1,000 µS/cm. Some meters also show CF (conductivity factor), where CF = EC in mS/cm × 10.