TDS Calculator
Calculate total dissolved solids in water using measured values and get a quick estimate of water quality.
Estimate total dissolved solids (TDS) in water from electrical conductivity using a conversion factor. This is an estimate, not a lab result.
About TDS & Conversion Factors
What is TDS? Total Dissolved Solids (TDS) measures the combined content of inorganic and organic substances dissolved in water.
Why do conversion factors vary? Different water compositions (natural water, tap water, wastewater) have different relationships between conductivity and TDS. Common factors range from 0.5 to 0.67.
Important: This tool provides an estimate only. For accurate TDS measurement, use a calibrated TDS meter or send samples to a lab.
What Is a TDS Calculator?
A TDS calculator estimates the total dissolved solids in a water sample. Total dissolved solids refer to the combined content of all inorganic and organic substances present in water, including minerals, salts, metals, and ions. This measurement is a key indicator of water quality, used in drinking water analysis, aquariums, hydroponics, and industrial water treatment.
The calculator typically uses an electrical conductivity (EC) reading or a direct TDS input to provide an estimated parts-per-million (ppm) value. Because TDS correlates strongly with conductivity, this method offers a fast, practical way to assess water purity without laboratory equipment.
How the TDS Calculation Works
The relationship between electrical conductivity and total dissolved solids is approximately linear for most natural waters. The standard conversion formula is:
TDS (mg/L) = EC (µS/cm) × Conversion Factor
The conversion factor depends on the water's ionic composition. Common values include:
- 0.5 – used for sodium chloride dominated waters (typical for many freshwater sources)
- 0.64 – used for mixed salt solutions (common in natural waters)
- 0.7 – used for potassium chloride based calibrations
If you input a TDS value directly, the calculator may also estimate the corresponding electrical conductivity using the inverse of the same factor. The accuracy of the estimate depends on how closely the actual water composition matches the assumed conversion factor.
How to Use the TDS Calculator
- Measure the electrical conductivity of your water sample using a calibrated EC meter. Record the value in microsiemens per centimeter (µS/cm) or millisiemens per centimeter (mS/cm).
- Select the appropriate conversion factor based on your water type. If unsure, 0.5 is a reasonable default for general freshwater.
- Enter the EC value and conversion factor into the calculator. The tool will output the estimated TDS in parts per million (ppm) or milligrams per liter (mg/L).
- Alternatively, if you already have a TDS reading, you can input that value to estimate the corresponding EC.
Example Calculation
Suppose you measure the electrical conductivity of a tap water sample and get a reading of 400 µS/cm. Using a conversion factor of 0.5:
TDS = 400 × 0.5 = 200 ppm
This suggests the water contains approximately 200 mg/L of dissolved solids. For comparison, typical drinking water ranges from 50 to 500 ppm, while reverse osmosis purified water may be below 50 ppm.
Understanding Your Results
TDS values provide a general indication of water quality, but they do not identify specific contaminants. A high TDS reading may indicate high mineral content, which is not necessarily harmful, or it could signal pollution from dissolved salts or metals. Low TDS water may taste flat and can be more corrosive to plumbing.
Common reference ranges for TDS in drinking water:
- Below 50 ppm – very low; typical of distilled or reverse osmosis water
- 50–150 ppm – low; common in many natural springs and filtered water
- 150–300 ppm – moderate; typical for most tap water
- 300–500 ppm – high; may have noticeable taste or hardness
- Above 500 ppm – very high; may indicate poor water quality or contamination
Always interpret TDS results alongside other water quality tests, especially if you suspect specific contaminants like lead, nitrates, or bacteria.
Common Mistakes When Using a TDS Calculator
- Using the wrong conversion factor – Different water compositions require different factors. Using 0.5 for seawater, for example, will produce inaccurate results.
- Ignoring temperature effects – Electrical conductivity varies with temperature. Most meters compensate automatically, but if yours does not, the reading may be off.
- Confusing units – EC is often reported in µS/cm or mS/cm (1 mS/cm = 1000 µS/cm). Mixing these up leads to order-of-magnitude errors.
- Assuming TDS equals water safety – A low TDS does not guarantee safe water, and a high TDS does not always indicate danger. TDS is one metric among many.
Limitations of TDS Estimation
The conversion from conductivity to TDS is an approximation. It assumes that all dissolved solids are ionic and that the relationship between conductivity and concentration is linear. In reality, different ions contribute differently to conductivity, and non-ionic dissolved solids (such as organic compounds) are not detected by this method. For precise regulatory compliance or scientific research, gravimetric analysis or ion-specific testing is required.
The calculator provides a useful estimate for routine monitoring, but it should not replace certified laboratory analysis when accuracy is critical.
Practical Use Cases
- Drinking water quality checks – Quickly assess whether your tap water falls within acceptable TDS ranges.
- Aquarium maintenance – Monitor TDS to maintain stable water conditions for fish and plants.
- Hydroponics – Ensure nutrient solution concentrations are within optimal ranges for plant growth.
- Reverse osmosis system performance – Compare feed water and product water TDS to evaluate membrane efficiency.
- Industrial water treatment – Track changes in water quality during processing or before discharge.
FAQ
What is a good TDS level for drinking water?
Most health guidelines recommend TDS levels below 500 ppm for drinking water. Water between 50 and 150 ppm is often considered ideal for taste and mineral content. Levels above 500 ppm may have noticeable taste or indicate potential quality issues.
Can I use a TDS meter instead of a calculator?
A TDS meter directly measures conductivity and applies a built-in conversion factor to display TDS. A calculator gives you more control over the conversion factor and helps you understand the underlying relationship. Both methods are valid, but a calculator is useful when you need to adjust the factor for specific water types.
Does TDS measure hardness?
Not directly. TDS measures total dissolved solids, which includes hardness-causing minerals like calcium and magnesium, but also includes other salts and organic matter. Water hardness is a specific measure of calcium and magnesium ions. High TDS often correlates with hard water, but the two are not identical.
Why does my TDS reading change with temperature?
Electrical conductivity increases as temperature rises because ions move more freely in warmer water. Most modern EC meters include automatic temperature compensation (ATC) to correct readings to a standard temperature, usually 25°C. If your meter lacks ATC, you should measure at a consistent temperature or apply a correction factor.
Is low TDS water safe to drink?
Low TDS water is not necessarily unsafe, but it may lack beneficial minerals and can taste flat. Some studies suggest that very low TDS water (below 50 ppm) may be more aggressive to plumbing and may not provide adequate mineral intake. Always test for specific contaminants rather than relying solely on TDS.