TDS Calculator — Total Dissolved Solids in Water
Enter the EC reading from your TDS meter to get the TDS in ppm (mg/L) and a drinking-water quality rating based on EPA and WHO guidelines.
µS/cm
Good — Well within recommended range
- 1
EC reading
400Electrical conductivity from the meter in µS/cm. - 2
TDS = EC × K
400 × 0.64 = 256
这个计算器是如何工作的？
TDS (ppm) = EC (µS/cm) × K. K is typically 0.5 for NaCl calibrated meters, 0.64 for general tap water, or 0.7 for KCl. The US EPA secondary limit is 500 ppm; WHO guideline is 500 ppm. Below 50 ppm may lack minerals; above 1,000 ppm is unsuitable for drinking. EC meters estimate TDS — gravimetric lab tests are the reference method.
公式
How this is calculated
TDS (Total Dissolved Solids) is the combined concentration of all dissolved inorganic and organic substances in water — salts, minerals, metals and organic matter — reported in ppm (parts per million) or mg/L, which are numerically equivalent for water. A TDS or EC meter does not measure solids directly; it measures electrical conductivity (EC) in microsiemens per centimetre (µS/cm), because dissolved ions carry electrical charge. TDS is then estimated as TDS ≈ EC × K, where K is an empirically determined conversion factor that accounts for the ionic composition of the water.
K varies with the type of dissolved ions: K ≈ 0.5 is used for sodium chloride (NaCl) calibration solutions, which is the factory default for most consumer meters; K ≈ 0.64 is the standard for general potable water with a typical ion mix; K ≈ 0.7 is used with potassium chloride (KCl) standards and some laboratory instruments. If your meter label says "NaCl calibration", use K = 0.5 or 0.64 depending on your source water. The default 0.64 is a reasonable starting point for most tap and well water.
Quality benchmarks: the US EPA Secondary Drinking Water Regulation recommends a maximum of 500 ppm for aesthetic reasons; the WHO guideline is also 500 ppm. TDS below 50 ppm (e.g., RO or distilled water) may taste flat and lack beneficial calcium and magnesium. Very low TDS does not guarantee safety — bacteria and many pesticides have negligible effect on conductivity. A lab gravimetric test (APHA Method 2540C) is the reference method for TDS; EC meters provide an estimate.
常见问题
It is not immediately harmful in most healthy adults, but WHO does not recommend long-term consumption of very low-mineral water without remineralisation. Reverse osmosis and distilled water in this range may taste bland and lack beneficial calcium and magnesium.
TDS meters estimate dissolved solids from conductivity using a fixed K factor. If the actual ionic composition differs from the calibration standard, the meter result diverges from a gravimetric lab test. For accurate measurements, use K = 0.64 for natural water and K = 0.5 for NaCl-dominated water.
Not necessarily. Natural mineral water can have TDS > 500 ppm from beneficial minerals. TDS measures quantity of dissolved matter, not which ions are present or whether they are harmful. For safety, test for specific contaminants (lead, nitrates, bacteria) separately.
也称为
TG we-Calculate Editorial Team. (2026). TDS Calculator — Total Dissolved Solids in Water [Online calculator]. TG we-Calculate. https://we-calculate.com/zh/calculator/tds-calculator
TG we-Calculate Editorial Team. "TDS Calculator — Total Dissolved Solids in Water." TG we-Calculate. 2026. https://we-calculate.com/zh/calculator/tds-calculator.
TG we-Calculate Editorial Team, "TDS Calculator — Total Dissolved Solids in Water," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/zh/calculator/tds-calculator
@misc{wecalculate_tds_calculator, title = {TDS Calculator — Total Dissolved Solids in Water}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/zh/calculator/tds-calculator}}, year = {2026}, note = {TG we-Calculate} }
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