EC to PPM Calculator
Convert between EC in mS/cm and PPM (TDS) for a nutrient solution. Enter one value and choose the 500, 640 or 700 scale your meter uses to get the matching reading.
How to convert EC and PPM
- Enter either an EC reading in mS/cm or a PPM reading.
- Choose the TDS scale your meter uses: 500, 640 or 700.
- Read the converted value and the conversion factor used.
Examples
EC 2.0 on the 500 scale
EC 2.0 mS/cm, 500 scale
1000 ppm (factor 500)
Frequently asked questions
Why do PPM meters disagree with each other?
PPM is derived from EC using a conversion factor that varies by brand. Common scales are 500 (Hanna, many US meters), 640 (Eutech) and 700 (Truncheon). The same EC reads as different PPM on each scale.
Which scale should I use?
Match the scale to your meter so your readings line up with your nutrient chart. If a feeding chart lists PPM, check which scale it assumes, since 1000 ppm on the 500 scale is not the same EC as 1000 ppm on the 700 scale.
What units does EC use here?
EC is entered in millisiemens per centimeter (mS/cm), the common range for hydroponic solutions. Some meters show microsiemens (uS/cm); divide those by 1000 to get mS/cm first.
Is this an exact lab measurement?
No. These are general conversion guidelines. Actual dissolved solids depend on the specific salts in solution, and temperature affects EC, so treat the result as a planning aid and trust a calibrated meter.
What EC or PPM should my plants be at?
Targets vary by crop and growth stage, so follow your nutrient brand and crop guidance. This tool only converts between EC and PPM and does not recommend a feeding strength.
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