Identify an unknown ppm scale
If a meter shows EC and ppm for the same sample, use the pair to estimate its conversion factor.
EC-first conversion
EC → displayed ppm/TDS
EC is the underlying conductivity measurement. Displayed ppm/TDS is a meter convention derived from EC.
Supported journal range: 0–20 mS/cm (0–20,000 µS/cm).
01.0 mS/cm2.03.0+
The visual bar is a magnitude display only. It is not a universal feeding target.
Reverse conversion
Displayed ppm/TDS → EC
500 conventionppm ≈ EC × 500
640 approximationTDS ≈ EC × 640; commonly used as an approximate irrigation-water TDS conversion.
650 meter conventionppm ≈ EC × 650 on meters/references using that factor.
700 conventionppm ≈ EC × 700
EC remains EC1 mS/cm = 1000 µS/cm = 1 dS/m; CF is commonly EC × 10.
Two meters can display different ppm values for the same conductivity if they use different conversion factors. Preserve EC and units whenever possible. These ppm/TDS values are conversion estimates, not a laboratory gravimetric measurement of total dissolved solids.
Solution increase above source water
Compare the final nutrient solution with the starting water. This is a conductivity difference only; it does not identify nutrient ions.
What EC tells you
Electrical conductivity reflects how readily the solution conducts current. It is influenced by dissolved ions but does not identify which ions are present or whether the nutrient balance is appropriate.
Method and temperature matter
- Keep the meter clean and calibrated as specified.
- Conductivity changes with temperature; record sample temperature and whether the meter reports temperature-compensated conductivity, commonly normalized to 25 °C.
- Use the same sample method and compensation convention when comparing trends.
Keep the context
Save water source, nutrient recipe, pH, irrigation event, sample type, plant stage, and meter scale beside the reading. A number without method and context is difficult to compare later.
Related plant references
Use Plant Atlas for anatomy and plant-structure context and Terpene Atlas for chemistry reference. These support interpretation but do not replace calibrated water measurements.
EC / TDS measurement journal
Save repeatable conductivity readings with meter, scale and sample context. Records stay in this browser unless exported.
Calibration date not recordedVerify the meter with the standard and procedure specified by its manufacturer before relying on a reading.
Reference check: 1.413 mS/cm (1413 µS/cm) is a common conductivity reference. It would display about 707 ppm at ×500, 904 ppm at ×640, 918 ppm at ×650, or 989 ppm at ×700. Use the certified value and reference temperature printed on your standard, and follow the meter manufacturer for the required procedure.
No measurements saved yet.
| Date | EC mS/cm | 500 ppm | 640 TDS | 650 ppm | 700 ppm | Sample | Meter | Calibration | Temp °C | Notes |
|---|
0 saved records. Record the original conductivity and meter convention whenever displayed ppm is used.