Chemical Oxygen Demand (COD) Calculator

COD measures the oxygen needed to chemically oxidize organics in water.

How the Math Works

The Chemical Oxygen Demand (COD) Calculator uses a straightforward mathematical formula to quantify water quality. COD equals the difference between a blank titration reading and a sample titration reading, multiplied by the solution's normality (N) and a conversion factor of 8000, then divided by the sample volume in milliliters. The blank reading accounts for any oxygen consumed during the titration process itself, ensuring only the sample's organic matter is measured. This calculation effectively converts chemical titration data into a standardized measure of organic pollution in water.

Practical Applications

To apply this calculation, first perform a titration using a standard potassium permanganate (KMnO4) solution on both your water sample and a blank (pure distilled water). Record the volume of titrant used for each. Measure your sample's volume precisely, and determine the normality of your KMnO4 solution. Input these three values—the blank volume, sample volume, and titrant normality—into the calculator. The result gives you the COD in milligrams of oxygen per liter (mg/L), allowing direct comparison with regulatory standards or treatment plant capacity.

Day-to-Day Use

This calculation helps protect your community's water quality in everyday ways. When evaluating drinking water sources, COD readings can indicate industrial pollution or agricultural runoff affecting your supply. At home, you can use it to assess if your septic system is functioning properly by testing drain field effluent. Municipalities rely on COD data to optimize water treatment processes, ensuring cleaner tap water. Even aquarium hobbyists use COD measurements to monitor tank water quality and adjust filtration systems for healthy fish populations.

Worked example

(20 − 12) × 0.1 × 8000 ÷ 20 → 320 mg/L.

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