TDS to Conductivity Calculator (EC µS/cm to ppm, mg/L)
By Santaji GadepatilinUpdated November 8, 2026
Conductivity meters measure how well water carries current, and total dissolved solids are estimated from it with a conversion factor of about 0.5–0.7. This TDS to conductivity calculator converts EC in µS/cm to TDS in mg/L (ppm), first correcting the reading to 25 °C, and works in reverse to give the conductivity for a target TDS — see how electrical conductivity and a conductivity sensor work.
How to use the TDS to conductivity calculator
Enter the measured conductivity in µS/cm, the water temperature and the temperature coefficient (2 %/°C is typical; enter 0 if your meter already shows a 25 °C compensated value), then the TDS factor. The calculator gives the conductivity at 25 °C and the TDS in mg/L (ppm). To find the conductivity that corresponds to a target TDS, enter the TDS and press × on the measured conductivity.
TDS and conductivity formulas
EC25 = ECT ÷ [1 + α (T − 25 °C)] · TDS = k × EC25
The factor k depends on which ions are dissolved: about 0.5 for NaCl, 0.55–0.7 for most fresh waters, and up to 0.8 for waters rich in sulphate. For accurate work, calibrate k against a gravimetric TDS test (evaporation at 180 °C) for your water.
Worked example
A sample reads 750 µS/cm at 20 °C (α = 2 %/°C, k = 0.65):
- EC25 = 750 ÷ [1 + 0.02 × (20 − 25)] = 750 ÷ 0.9 = 833.3 µS/cm
- TDS = 0.65 × 833.3 = 542 mg/L — rated “good” for taste and just above India’s 500 mg/L acceptable limit
Typical conductivity and TDS
| Water | Conductivity (25 °C) | TDS, k = 0.5 | TDS, k = 0.65 | TDS, k = 0.7 |
|---|---|---|---|---|
| Pure (RO / distilled) water | 5 µS/cm | 2 mg/L | 3 mg/L | 4 mg/L |
| Rain water | 50 µS/cm | 25 mg/L | 32 mg/L | 35 mg/L |
| Soft tap water | 200 µS/cm | 100 mg/L | 130 mg/L | 140 mg/L |
| Typical tap water | 500 µS/cm | 250 mg/L | 325 mg/L | 350 mg/L |
| Hard ground water | 1,000 µS/cm | 500 mg/L | 650 mg/L | 700 mg/L |
| Brackish water | 5,000 µS/cm | 2,500 mg/L | 3,250 mg/L | 3,500 mg/L |
| Sea water | 53,000 µS/cm | 26,500 mg/L | 34,450 mg/L | 37,100 mg/L |
Values are typical; real samples vary widely.
Practical notes
- 1 mS/cm = 1,000 µS/cm; some meters show EC in mS/cm or dS/m (1 dS/m = 1 mS/cm), and hydroponic “CF” units are EC in mS/cm × 10.
- Different TDS meters use different built-in factors (0.5 “NaCl”, 0.7 “442”), so two meters can show different ppm for the same water — compare EC, not ppm.
- Conductivity is not a measure of purity against non-ionic contaminants: sugar, oils and many organics do not conduct and are not counted.
- Keep the conductivity cell clean and calibrated with a standard (e.g. 1,413 µS/cm KCl); the cell constant drifts as electrodes foul.
Frequently asked questions
How do you convert conductivity to TDS?
TDS (mg/L) = k × EC (µS/cm at 25 °C), with k usually between 0.55 and 0.75 for natural waters. A factor of 0.5 is used for sodium chloride solutions and 0.65–0.7 for typical fresh water.
Is TDS in ppm the same as mg/L?
For dilute water, yes — 1 mg/L ≈ 1 ppm because a litre of water weighs about 1 kg. In sea water and brines the density is higher, so the two differ by a few percent.
Why does conductivity need temperature compensation?
Ions move faster in warm water, so conductivity rises by about 2% per °C. Readings are referred to 25 °C so that samples measured at different temperatures can be compared.
What TDS is safe for drinking water?
The WHO gives no health-based limit, but taste is rated excellent below 300 mg/L, good up to 600 and unacceptable above about 1,200. India's BIS IS 10500 sets 500 mg/L as acceptable and 2,000 mg/L as permissible where no other source exists.