The Chemical Oxygen Demand Calculator is a scientific tool used to determine the amount of oxygen required to chemically oxidize organic and inorganic matter present in a water sample. COD is one of the most important indicators of water quality, wastewater strength, and pollution levels.
This calculator helps environmental professionals, researchers, and students quickly compute COD values based on titration or spectrophotometric data, eliminating manual errors and saving laboratory time.
Chemical Oxygen Demand (COD) measures the total quantity of oxygen needed to oxidize organic pollutants in water using a strong chemical oxidant. It is widely used in environmental engineering, wastewater treatment, and regulatory monitoring to assess pollution levels.
Higher COD values indicate greater pollution and higher oxygen demand, which can harm aquatic life by reducing dissolved oxygen levels in natural water bodies.
Below are the core equations used in COD determination:
COD (mg/L) = (A − B) × N × 8000 / V
Where:
A = Volume of titrant used for blank (mL)
B = Volume of titrant used for sample (mL)
N = Normality of titrant
V = Volume of water sample (mL)
Oxygen Equivalent:
1 mole O₂ = 32 g oxygen
Oxidation Principle (Dichromate Method):
Organic Matter + Cr₂O₇²⁻ + H⁺ → CO₂ + H₂O + Cr³⁺
These relationships quantify how much oxygen would be required to oxidize contaminants in the sample.Suppose the following titration data:
Blank titration (A) = 10.2 mL
Sample titration (B) = 4.6 mL
Titrant normality (N) = 0.1 N
Sample volume (V) = 50 mL
Step 1:
Subtract titration values → (A − B) = 5.6 mL
Step 2:
Multiply by normality → 5.6 × 0.1 = 0.56
Step 3:
Apply formula → COD = (0.56 × 8000) ÷ 50
Result: COD = 89.6 mg/L
This indicates moderate organic pollution in the water sample.