TDS to Electrical Conductivity (EC) Converter

TDS to EC Converter: Switch Between Conductivity and Dissolved Solids in Seconds

This free tool converts a water conductivity reading (EC) into Total Dissolved Solids (TDS), or the other way round, in whichever units your meter, lab report or dosing chart happens to use. Enter one value, pick a conversion factor, and it hands back the other value instantly, along with a plain-language water-quality read and an irrigation salinity read — both worked out with full, visible step-by-step math so you're never just trusting a black box.

It's built for anyone who deals with water numbers day to day: RO and water-treatment plant operators, aquarium and pond keepers, hydroponic and coco-coir growers, agriculture and irrigation staff, lab technicians, and students learning water chemistry. The conversion logic matches what handheld TDS and EC meters use internally, so the number you get here should line up closely with what your own meter shows.

TDS and EC: What They Actually Mean

Total Dissolved Solids is the total weight of everything dissolved in water that isn't water itself — mainly minerals and salts like calcium, magnesium, sodium, potassium, bicarbonates, sulfates and chlorides. It's usually measured in milligrams per litre (mg/L), which for water is the same as parts per million (ppm).

Electrical Conductivity measures how well water carries an electric current. Pure water barely conducts electricity at all, but the moment salts dissolve into it, they split into charged ions that carry current very efficiently. So the more dissolved solids there are, the higher the conductivity — which is exactly why a cheap conductivity probe can be used as a fast, indirect way to estimate TDS without running a full lab test.

Why Convert Between TDS and EC at All?

Most affordable handheld water meters measure conductivity directly — it's a simple electrical measurement — and then apply a built-in conversion factor to display an estimated TDS number on the screen. Lab reports, nutrient charts, and drinking-water standards sometimes quote TDS, and sometimes quote EC, so it's genuinely common to have one number and need the other.

This matters in practice because different industries default to different units. Hydroponic growers usually think in EC (often in mS/cm). Drinking-water guidelines and RO/DI enthusiasts usually think in TDS (ppm). Agricultural and irrigation-water testing leans on EC in dS/m. This converter lets you move freely between all of them without hunting down the right formula every time.

The TDS to EC Conversion Formula

The relationship between the two is a simple, direct proportion:

TDS (mg/L) = EC (µS/cm) x conversion factor

And the reverse direction is just as simple:

EC (µS/cm) = TDS (mg/L) ÷ conversion factor

The only tricky part is the conversion factor itself — it isn't one fixed number, because it depends on exactly which salts are dissolved in the water.

Which Conversion Factor Should You Use?

The conversion factor changes depending on the mix of ions in the water, because different salts conduct electricity slightly differently for the same dissolved mass. There's no single number that's technically correct for every water source — but a handful of standard factors cover almost every real situation:

• 0.5 (NaCl reference) — best for water where sodium chloride dominates, such as coastal, brackish or seawater-influenced sources.
• 0.64 (the "442" factor, Standard Methods 2510B) — the general-purpose default used by most municipal water reports and lab certificates when no specific factor is stated.
• 0.55 (KCl reference) — common as a factory default on many consumer TDS meters, especially ones calibrated with potassium chloride solution.
• 0.70 — a better fit for hard water with high calcium and magnesium content, which is common in borewell water and some hydroponic nutrient blends.

Worked Example: Converting EC to TDS

Say your meter reads 750 µS/cm on a tap water sample, and you're using the standard 0.64 factor. TDS = 750 x 0.64 = 480 mg/L. That value falls squarely in the "Good" band on the drinking-water TDS scale — a perfectly normal, palatable result for municipal tap water.

Now try the same reading with the 0.5 (NaCl) factor instead: TDS = 750 x 0.5 = 375 mg/L. Notice the answer changes meaningfully just from picking a different factor — which is exactly why it's worth knowing which factor your meter, lab or use case actually calls for, rather than assuming they're all interchangeable.

Why Temperature Changes Your EC Reading

Conductivity is temperature-sensitive: warmer water lets ions move faster, so the same water reads a higher EC when it's warm than when it's cool — roughly 2% higher for every 1°C above the standard reference temperature of 25°C. A reading taken from a warm tank or a hot borewell sample can therefore look artificially high unless it's corrected back to that 25°C reference point.

Most modern meters have automatic temperature compensation (ATC) built in and handle this correction for you. If your meter doesn't, or if you're working from a raw, uncompensated reading, this calculator's advanced temperature option applies the same 2% per °C correction so the TDS or classification result stays accurate regardless of the water's temperature when it was measured.

Reading the Water-Quality Scale (TDS)

For drinking and general household water, TDS is commonly interpreted on a five-band scale: below 300 mg/L is excellent, 300 to 600 mg/L is good, 600 to 900 mg/L is fair, 900 to 1,200 mg/L is poor, and anything above 1,200 mg/L is considered unacceptable for regular drinking use. This calculator applies that scale automatically to whichever TDS value it works out.

It's worth remembering that TDS on its own doesn't say what's dissolved — only how much. Two samples with an identical TDS number can taste, behave and affect health completely differently depending on whether the dissolved solids are mostly harmless minerals like calcium and magnesium, or something more concerning like nitrates or heavy metals. TDS is a fast screening number, not a full water-safety test.

Reading the Salinity Hazard Scale (EC, for Irrigation)

For irrigation water specifically, EC is read on a different scale — the widely used US Salinity Laboratory (USSL) bands: below 0.25 dS/m is a low salinity hazard, 0.25 to 0.75 dS/m is medium, 0.75 to 2.25 dS/m is high, and above 2.25 dS/m is a very high salinity hazard. This calculator shows this classification alongside the TDS result any time you convert a value, since the same reading is often relevant to both a household-water and a farm-water decision.

A high salinity hazard doesn't mean water can never be used for irrigation — it means the crop, soil drainage and leaching practices all need to be chosen carefully to avoid salt build-up in the root zone over repeated irrigation cycles.

How a TDS/EC Meter Actually Measures Water

A conductivity meter works by sending a small, safe electrical current between two metal probes sitting in the water and measuring how easily that current passes through. The instrument itself never measures dissolved solids directly — it measures conductivity, then runs that number through a conversion factor programmed into its firmware to display a TDS estimate on the screen.

This is exactly why two different meters can show two different TDS numbers on the very same glass of water: they may simply be using different built-in conversion factors. It's also why a cheap meter reading and a certified lab's gravimetric TDS test (where water is literally evaporated and the leftover residue weighed) can disagree slightly — the meter is always giving you an estimate, not a direct measurement, and this converter is built to make that estimate step transparent instead of hidden inside a black box.

TDS and EC in RO Systems and Water Treatment

Reverse osmosis (RO) systems are usually judged by how much they drop the TDS or EC of the incoming water, since that drop is a direct, easy-to-measure sign of how well the membrane is filtering out dissolved salts. A common rule of thumb is the rejection rate: (feed water TDS − permeate/output TDS) ÷ feed water TDS × 100, and a healthy home RO membrane typically rejects somewhere around 90 to 98% of incoming dissolved solids.

Because RO controllers, feed-water reports, and permeate-quality specs don't all standardize on the same unit, converting between TDS and EC on both sides of the membrane is a routine part of monitoring an RO system's health, spotting a failing membrane early, and deciding when it's time for a service or replacement, well before output water quality drops low enough to be noticeable by taste alone.

TDS/EC in Hydroponics, Aquariums, and Ponds

Hydroponic and coco-coir growers dose nutrients by EC rather than TDS in most cases, because EC responds instantly and consistently to a probe, while TDS depends on which conversion factor the grower's meter happens to use. Even so, many nutrient charts and forums still quote target ranges in ppm, which is exactly where a quick, reliable converter earns its keep — translating a chart's ppm target into the EC number your meter actually needs to hit, or vice versa.

Aquarium and pond keepers use the same conversion for a slightly different reason: many fish, shrimp and coral species have a narrow TDS or hardness range they tolerate well, and test kits or meters sometimes report in one unit while the species guide reports in another. Converting once, correctly, avoids under- or over-dosing minerals or accidentally shocking sensitive livestock with an unintended TDS swing.

Typical TDS and EC Values for Common Water Sources

Having a few real-world reference points makes it much easier to sanity-check a fresh reading against what's actually normal, so here's roughly where common water sources tend to fall (using the general 0.64 factor):

• Reverse osmosis / distilled water: 0 - 50 mg/L TDS (0 - 80 µS/cm) — very low, close to pure water.
• Rainwater: 20 - 80 mg/L TDS (30 - 125 µS/cm) — naturally soft, low in dissolved minerals.
• Municipal tap water: 150 - 500 mg/L TDS (235 - 780 µS/cm) — varies a lot by region and source.
• Borewell / groundwater: 300 - 1,500 mg/L TDS (470 - 2,340 µS/cm) — usually higher due to mineral contact with rock and soil.
• Brackish water: 1,000 - 10,000 mg/L TDS — noticeably salty, unsuitable for drinking without treatment.
• Seawater: roughly 35,000 mg/L TDS (about 50,000 µS/cm) — far beyond drinking-water range on any scale.

Common Mistakes When Converting TDS and EC

The single most common mistake is mixing up units — treating a µS/cm reading as if it were mS/cm, which is a 1,000x error, or forgetting that 1 mS/cm equals 1 dS/m exactly. Always double-check which unit a meter, chart or lab report is actually using before typing a number in.

The second common mistake is assuming one universal conversion factor applies everywhere. A factor of 0.5 and a factor of 0.7 on the same EC reading can shift the resulting TDS by 40% or more — which is easily enough to move a result from one water-quality band into a completely different one. When in doubt, check your meter's manual or your lab report for the exact factor it uses, and stay consistent with that same factor for before-and-after comparisons.

The third mistake is ignoring temperature on a meter without automatic compensation. A sample measured straight out of a warm tank, without correcting to the 25°C reference, can read noticeably higher than the water's true, stable EC — which matters most when tracking small changes over time, like slowly rising salinity in a reused hydroponic reservoir.

TDS to EC Converter: Quick Reference Summary

TDS (mg/L) = EC (µS/cm) x conversion factor. EC (µS/cm) = TDS (mg/L) ÷ conversion factor. Common factors: 0.5 (NaCl), 0.55 (KCl), 0.64 (general/"442"), 0.7 (hard water). Unit shortcuts: 1 mS/cm = 1 dS/m = 1,000 µS/cm, and 1 g/L = 1,000 mg/L. Drinking-water TDS bands: excellent below 300, good 300-600, fair 600-900, poor 900-1,200, unacceptable above 1,200 mg/L. Irrigation salinity (EC, dS/m): low below 0.25, medium 0.25-0.75, high 0.75-2.25, very high above 2.25.

This calculator is built to support everyday water testing, learning, and field decisions. For anything with real stakes attached — a municipal supply, a commercial farm's irrigation source, or drinking water for a household — always confirm results against a certified water-testing laboratory rather than a meter or converter alone.