💧 Water & hydroponics
PPM to EC Converter
Convert TDS ppm to EC in µS/cm or mS/cm using the 0.5, 0.64 or 0.7 conversion scale. Enter a value and choose the scale, then press Convert.
About the PPM to EC Converter
Electrical conductivity measures how well water carries current, which depends on dissolved ions. TDS meters infer ppm from EC with an assumed factor. The three common scales are 0.5 (1 µS/cm = 0.5 ppm), 0.64 (the NaCl approximation) and 0.7. Two meters reading the same water can therefore differ by 40% without either being broken.
EC is the more reproducible measurement because it is not derived. If you are following a nutrient chart, use the scale the chart specifies. For hydroponics, record EC and the scale alongside the number; a bare 'ppm' figure is ambiguous.
How the calculation works
- ppm = EC (µS/cm) × scale factor.
- EC (µS/cm) = ppm ÷ scale factor.
- 1 mS/cm = 1,000 µS/cm.
- Common scales: 0.5, 0.64 and 0.7.
Reference values
| EC (µS/cm) | 0.5 scale | 0.64 scale | 0.7 scale |
|---|---|---|---|
| 500 | 250 ppm | 320 ppm | 350 ppm |
| 1,000 | 500 ppm | 640 ppm | 700 ppm |
| 1,500 | 750 ppm | 960 ppm | 1,050 ppm |
| 2,000 | 1,000 ppm | 1,280 ppm | 1,400 ppm |
| 2,500 | 1,250 ppm | 1,600 ppm | 1,750 ppm |
Worked example: the same water on three scales
A meter reading 1,400 µS/cm at the 0.5 scale reports 700 ppm. The same water at 0.64 is 896 ppm, and at 0.7 it is 980 ppm. If a nutrient chart says 1.2 EC (mS/cm) and your meter uses 0.5, the target is 600 ppm—not 1,200.
That is why a bare “ppm” figure is ambiguous. Record EC and the conversion factor together, or use EC directly. The meter is measuring conductivity, not a count of dissolved solids; the ppm number is an inference based on an assumed mix of ions.