TDS from Conductivity Calculator
Total dissolved solids in water from an electrical-conductivity reading — with the conversion factor for the kind of water, temperature compensation to 25 °C, and what the result means for drinking, irrigation or an aquarium.
Dissolved salts carry current, so conductivity tracks TDS: TDS (mg/L) = EC (µS/cm) × a factor between 0.
How the tds from conductivity calculator works
Dissolved salts carry current, so conductivity tracks TDS: TDS (mg/L) = EC (µS/cm) × a factor between 0.5 and 0.7 depending on which ions dominate — 0.5 for sodium-chloride-type water and cheap meters, 0.64 as a general natural-water value, 0.7 for hard, sulphate-rich water. Conductivity rises about 2% per °C, so a reading taken away from 25 °C is corrected first.
Formula: EC₂₅ = EC ÷ (1 + 0.02 × (T − 25)); TDS = EC₂₅ × factor
Worked examples
| Inputs | Total dissolved solids | Note |
|---|---|---|
| 800 µS/cm at 25 °C, general water | 512 mg/L | 512 mg/L — good |
| Same reading at 15 °C | 640 mg/L | 640 mg/L after compensation |
| A meter reading in 0.5 mode | 750 mg/L | 750 mg/L |
FAQFrequently asked questions
Which factor should I use?
Handheld TDS meters mostly use 0.5 (calibrated to NaCl); 0.64–0.7 is closer for river, tap and bore water rich in calcium, magnesium and sulphate. If you have a lab TDS result, divide it by your EC to get the factor for your water.
What TDS is safe to drink?
The WHO gives no health limit; palatability is the issue. Under 300 mg/L is excellent, 300–600 good, 600–900 fair, 900–1,200 poor and above 1,200 unacceptable to most people. Very low TDS (under 50) tastes flat.
Why compensate for temperature?
Ions move faster in warm water, so the same salt content reads about 2% higher per degree. Meters with ATC do this automatically; a raw reading at 15 °C is 20% low.
Is TDS the same as hardness?
No. Hardness counts only calcium and magnesium; TDS counts all dissolved ions. Hard water has high TDS, but high TDS can be sodium and chloride with little hardness.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- CSIRO — Australia's national science agency
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.