Calculator
Example Data Table
The table shows how the same TDS changes EC when the factor changes.
| TDS (ppm) | Factor | EC (µS/cm) | EC (mS/cm) |
|---|---|---|---|
| 300 | 0.5 | 600.00 | 0.6000 |
| 500 | 0.5 | 1000.00 | 1.0000 |
| 700 | 0.7 | 1000.00 | 1.0000 |
| 900 | 0.64 | 1406.25 | 1.4063 |
| 1200 | 0.7 | 1714.29 | 1.7143 |
Formula Used
Many meters estimate TDS from EC using a scale factor:
Optional temperature compensation converts values to a 25°C reference:
Use α around 0.019 per °C for typical water. Adjust if your meter specifies a different coefficient.
How to Use This Calculator
- Choose TDS → EC if you have a ppm value.
- Pick the ppm scale factor your meter uses.
- Select your desired EC output unit.
- Enable temperature compensation if readings vary by season.
- Press Calculate to see results under the header.
- Use the CSV or PDF buttons to save your latest result.
Guide to Interpreting TDS and EC in Garden Water
1) What EC and TDS represent
Electrical conductivity (EC) reflects how well your water conducts electricity, which increases as dissolved ions rise. Total dissolved solids (TDS) is a meter-based estimate, usually reported as ppm (mg/L). Because ions vary, TDS is an approximation.
2) Why ppm scales matter
Many handheld meters convert EC to TDS using a factor such as 0.50, 0.64, or 0.70. For the same EC, these factors can change the displayed ppm by 40% or more. This calculator lets you match your meter’s scale so your logbook stays consistent.
3) Typical ranges gardeners track
Rainwater and RO water often measure under 0.10 mS/cm (100 µS/cm). Municipal supplies commonly fall near 0.20–0.80 mS/cm. Nutrient solutions can range from 1.0–2.4 mS/cm depending on crop stage and climate. Always confirm with your crop guide.
4) Temperature correction for better comparisons
EC rises with temperature. If you measure at 15°C in winter and 35°C in summer, the same water can appear different. Converting to a 25°C reference improves comparisons between weeks. A common coefficient is 0.019 per °C.
5) Practical decisions from the result
Use the EC output to adjust fertilizer strength, decide on dilution, or blend sources. For sensitive seedlings, keeping irrigation water below roughly 0.7 mS/cm can reduce stress, while higher readings may require monitoring runoff and leaf tip burn.
FAQs
1) Is TDS the same as EC?
TDS is an estimated ppm value derived from EC using a factor. EC is the direct conductivity measurement. Different solutions can share EC yet differ in actual dissolved mass.
2) Which factor should I choose?
Use the factor your meter uses. Many devices label 500, 640, or 700 scales. If unsure, test your meter by switching units or checking its manual, then match that value here.
3) Why can two meters show different ppm?
They may use different conversion factors, different temperature compensation, or different calibration solutions. PPM is not a universal standard; EC is usually more comparable between brands.
4) Should I enable temperature compensation?
If you log readings across seasons, enabling it helps keep results comparable at a 25°C reference. If your meter already compensates automatically, you can leave this off for consistency.
5) What unit is best: µS/cm or mS/cm?
They are the same measurement at different scales. Use µS/cm for low-salinity water and mS/cm for nutrient solutions. 1 mS/cm equals 1000 µS/cm.
6) Can I use this for hydroponics?
Yes, the EC output is useful for mixing nutrients. Keep in mind the chosen factor only affects the displayed ppm estimate; your dosing decisions should prioritize EC targets recommended for your crop.
7) Why is the result still an estimate?
EC responds to ions, not total mass. The ion mix (e.g., sodium, calcium, nitrates) changes how ppm relates to EC. The calculator provides the standard meter-style conversion for practical tracking.