If you’ve ever plugged your readings into a feeding chart and gotten numbers that don’t match, you’re not doing it wrong. Your meter and the chart are probably using different PPM scales, and nobody told you that was a thing. This EC to PPM converter handles the math in both directions and lets you pick the scale that matches your actual meter, so you stop second-guessing every reading.

EC (electrical conductivity) is the universal measurement. PPM (parts per million) is just EC translated into a number your nutrient chart can use, but there are three different translation scales in common use, and cheap TDS meters don’t tell you which one they’re using.

How to Use This Converter

Choose your conversion direction. Select EC to PPM if you have an EC reading and need a PPM value, or PPM to EC if you want to go the other way.
Select your PPM scale. Choose 500, 640, or 700. If you’re not sure which scale your meter uses, see the FAQ below.
Enter your value. Type in your EC (in mS/cm) or PPM reading.
Read the output. The converted value appears instantly. Use this number to cross-reference your feeding chart or dial in your nutrient solution.

Frequently Asked Questions

What is EC in hydroponics and why does it matter?

EC measures the total electrical conductivity of your nutrient solution, which tells you how concentrated it is. Water with dissolved salts and minerals conducts electricity better than pure water, so a higher EC means more nutrients are present. It’s the most reliable way to know whether your solution is too weak, dialed in, or strong enough to cause nutrient burn. Unlike PPM, EC doesn’t depend on any conversion scale, so it means the same thing no matter what meter you’re using.

What is the difference between EC and PPM?

EC is the raw measurement. PPM is a calculated estimate of dissolved solids based on that EC reading. The problem is there’s no single formula for the conversion; meter manufacturers settled on three different multipliers over the years (the 500, 640, and 700 scales), so the same water sample can show three different PPM values depending on which meter you use. EC is consistent across all meters and is what professional growers typically rely on. PPM is useful when your feeding chart is written in PPM, as long as you know which scale to match.

Which PPM scale should I use, 500 or 700?

It depends on your meter, not your preference. The 500 scale (also called the NaCl scale) is used by most budget TDS meters and some Hanna instruments. The 700 scale (also called the KCl scale) is used by Bluelab, Milwaukee, and most meters sold in hydroponic stores. The 640 scale is less common and used by some Truncheon meters. Check your meter’s manual or look up the model. If you can’t find it, test a known EC solution (like 1.0 mS/cm) and see whether your meter reads closer to 500 or 700 PPM. See the hydroponic EC chart for target ranges by crop and growth stage.

Why do my EC and PPM readings not match the feeding chart?

Almost always a scale mismatch. If your chart was written for the 700 scale and your meter uses the 500 scale, your readings will look about 28% lower than expected, which can push you to over-feed trying to hit the target. The fix is to either convert your reading to the right scale using this tool, or switch to reading EC only and use an EC-based feeding chart. You can learn more about dialing in your solution in how to feed hydroponic plants.

Is EC or PPM more accurate for hydroponics?

EC is more accurate and consistent. PPM is a derived value that introduces ambiguity the moment different scales exist. If your meter reads EC, use EC. Most modern feeding guides include both values, or you can use the hydroponic nutrient calculator to work backward from target EC to the right dose for your specific nutrients.

Once you know your meter’s scale and can convert confidently in both directions, you can stop relying on guesswork and start treating your nutrient solution like the precise input it actually is. For more calculators to dial in every other variable in your setup, browse the hydroponic tools collection.