TDS converter
Convert water conductivity to total dissolved solids. Pick the scale your meter uses: they disagree by up to 40% on the same water.
That's about the same as ordinary tap water. That is good drinking water, low in minerals.
What it means
How pure is that water?
A TDS meter does not measure solids. It measures conductivity and multiplies, so anything dissolved that does not conduct — sugar, for instance — is invisible to it.
Every unit
Your reading in every unit
Learn
Three things worth knowing
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ppm = µS/cm × 0.5 to 0.7
The NaCl scale uses 0.5, the hydroponic scale 0.64 and the 442 scale 0.7. Always note which scale a reading came from.
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Why 442
It stands for a mixture of 40% sodium sulfate, 40% sodium bicarbonate and 20% sodium chloride, chosen to imitate natural fresh water better than pure salt does.
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TDS is not purity
Mineral water has a high TDS and is perfectly good; water contaminated with a non-conducting toxin can read zero. TDS measures dissolved salts, nothing more.
Shortcuts
Popular dissolved solids conversions
Background
About TDS and conductivity
Dissolved salts make water conduct, so a cheap probe can estimate how much is in there. But it is only an estimate: the meter multiplies conductivity by a fixed factor, and manufacturers pick different ones.
The same 1000 µS/cm water reads 500 ppm on a NaCl meter and 700 ppm on a 442 meter. Neither is wrong; they answer slightly different questions.