EC ↔ PPM Converter
Use this calculator to convert electrical conductivity (EC) in mS/cm to ppm (TDS), or convert ppm back to EC.
What is an EC PPM calculator?
An EC PPM calculator helps growers, hydroponic gardeners, and water-quality users convert between two common concentration readings:
- EC (Electrical Conductivity) measured in mS/cm or µS/cm
- PPM (Parts Per Million), often shown as TDS on handheld meters
EC is a direct measurement of how well water conducts electricity. PPM is an estimate of dissolved solids. Because ppm is estimated from conductivity using a conversion factor, two meters can show different ppm values for the same solution.
How EC and PPM are related
Core formulas
- PPM = EC (mS/cm) × scale factor
- EC (mS/cm) = PPM ÷ scale factor
- µS/cm = EC (mS/cm) × 1000
Common scale factors are 500, 640, and 700. That means an EC value of 1.0 mS/cm could display as 500 ppm, 640 ppm, or 700 ppm depending on the meter setting.
Why different meters disagree
PPM is not a universal direct reading. It depends on the assumed dissolved salts model used by the device. For this reason, many professional growers track nutrients in EC first, then use ppm only when required for local conventions.
Quick reference conversion table
| EC (mS/cm) | PPM (500 scale) | PPM (640 scale) | PPM (700 scale) |
|---|---|---|---|
| 0.4 | 200 | 256 | 280 |
| 0.8 | 400 | 512 | 560 |
| 1.2 | 600 | 768 | 840 |
| 1.6 | 800 | 1024 | 1120 |
| 2.0 | 1000 | 1280 | 1400 |
How to use this EC ppm calculator
- Select conversion mode: EC to PPM or PPM to EC.
- Enter your reading.
- Choose your meter scale (500, 640, or 700).
- Click Calculate to see converted values and interpretation guidance.
If your meter manual is unclear, test with known calibration fluid or check the manufacturer documentation for the TDS factor.
Typical EC ranges for nutrient solutions
Target ranges vary by plant type, growth stage, light intensity, and environment, but these general bands are useful starting points:
- Seedlings / clones: 0.4–0.8 mS/cm
- Leafy greens: 0.8–1.6 mS/cm
- Herbs: 1.0–1.8 mS/cm
- Fruiting crops: 1.6–2.8 mS/cm
Always adjust gradually. Sudden EC jumps can stress roots and reduce uptake efficiency.
Common mistakes to avoid
- Comparing ppm values from different meters without matching scales.
- Ignoring water temperature (most meters auto-compensate, but not all).
- Using ppm alone without checking pH and overall nutrient balance.
- Assuming higher EC always means better growth.
EC vs TDS vs salinity
EC is measured directly, while TDS/ppm is estimated from EC. Salinity can be related, but it may be reported in different units (ppt, PSU, or conductivity-based indices) depending on industry standards.
FAQ
Which is better: EC or ppm?
EC is generally better for consistency because it is a direct measurement. ppm depends on scale assumptions.
What is the difference between 500 and 700 scales?
They use different conversion assumptions. For the same EC reading, a 700-scale meter reports a higher ppm value than a 500-scale meter.
Can I switch scales mid-grow?
Yes, but convert and log carefully. Keep one standard for your notes to avoid over- or under-feeding plants.