Chemical Oxygen Demand Calculator
Compute chemical oxygen demand using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
Calculator
Adjust values & calculateFormula
Where A is blank titrant volume (mL), B is sample titrant volume (mL), N is normality of FAS, V is sample volume (mL), D is dilution factor, and 8000 converts milliequivalents to mg O2/L.
Last reviewed: December 2025
Worked Examples
Example 1: Municipal Wastewater COD
Example 2: Industrial Effluent with Dilution
Background & Theory
The Chemical Oxygen Demand Calculator applies the following established principles and formulas. Chemistry is the science of matter's composition, structure, properties, and transformations. At the heart of quantitative chemistry lies the mole concept. One mole of any substance contains exactly 6.022×10²³ entities (Avogadro's number, Nₐ), and the molar mass of an element or compound in grams per mole is numerically equal to its atomic or molecular mass in atomic mass units. This allows chemists to convert between measurable mass and the number of reacting particles. Stoichiometry uses balanced chemical equations to relate the amounts of reactants and products. A balanced equation conserves both mass and charge. Molarity, the most common concentration unit, is defined as M = n/V, where n is moles of solute and V is volume of solution in liters, giving units of mol/L. Acidity and basicity are quantified by the pH scale, defined as pH = −log₁₀[H⁺], where [H⁺] is the molar concentration of hydrogen ions. Pure water at 25°C has pH 7.00; acids have lower values and bases higher values. Each unit change represents a tenfold change in hydrogen ion concentration. Gas behavior is described by the ideal gas law PV = nRT, where P is pressure in pascals, V is volume in cubic meters, n is moles, R = 8.314 J/(mol·K), and T is temperature in kelvin. Special cases include Boyle's Law (P₁V₁ = P₂V₂ at constant temperature) and Charles's Law (V₁/T₁ = V₂/T₂ at constant pressure). Thermochemistry quantifies heat changes in reactions through enthalpy, H. Hess's Law states that the total enthalpy change for a reaction is the sum of enthalpy changes for any sequence of steps leading to the same overall reaction, making it possible to calculate enthalpies for reactions that cannot be measured directly. Electron configuration describes the distribution of electrons in atomic orbitals according to the Aufbau principle, Pauli exclusion principle, and Hund's rule. Periodic trends including atomic radius, ionization energy, and electronegativity arise systematically from electron configuration and nuclear charge, enabling chemists to predict and rationalize chemical behavior across the periodic table.
History
The history behind the Chemical Oxygen Demand Calculator traces back through the following developments. Chemistry's roots lie in alchemy, the medieval practice combining proto-scientific experimentation with mystical aims. Alchemists developed practical techniques including distillation, calcination, and the preparation of acids, building a body of empirical knowledge despite their theoretical misunderstandings. Modern chemistry is conventionally dated to Antoine Lavoisier (1743–1794), often called the father of modern chemistry. Lavoisier demonstrated the law of conservation of mass in 1789, showing that matter is neither created nor destroyed in chemical reactions. He identified oxygen's role in combustion, dismantling the phlogiston theory, and co-authored the first systematic chemical nomenclature, establishing the language still used today. John Dalton proposed the first modern atomic theory in 1803, asserting that all matter is composed of indivisible atoms, that atoms of the same element are identical in mass, and that compounds form from fixed ratios of different atoms. This provided a physical basis for Lavoisier's conservation law and Proust's law of definite proportions. Dmitri Mendeleev published his periodic table in 1869, arranging the 63 known elements by atomic mass and revealing repeating patterns of chemical behavior. He boldly left gaps for undiscovered elements and predicted their properties with remarkable accuracy, predictions confirmed by the subsequent discovery of gallium, scandium, and germanium. Ernest Rutherford's gold foil experiment in 1911 revealed the nuclear model of the atom: a tiny, dense, positively charged nucleus surrounded by electrons. Niels Bohr refined this in 1913 with a quantized model of electron orbits that explained the hydrogen emission spectrum. Quantum chemistry and molecular orbital theory, developed through the 1920s and 1930s, provided the full quantum mechanical description of chemical bonding. The latter 20th century saw the rise of computational chemistry, enabling molecular simulation at unprecedented scale. The green chemistry movement, articulated in the 12 Principles of Green Chemistry in 1998, reoriented the field toward sustainability, waste reduction, and benign chemical design, reflecting chemistry's growing awareness of its environmental responsibilities.
Frequently Asked Questions
Formula
COD = ((A - B) * N * 8000) / V * D
Where A is blank titrant volume (mL), B is sample titrant volume (mL), N is normality of FAS, V is sample volume (mL), D is dilution factor, and 8000 converts milliequivalents to mg O2/L.
Worked Examples
Example 1: Municipal Wastewater COD
Problem: Blank titrant = 25.0 mL, Sample titrant = 10.5 mL, FAS normality = 0.25 N, Sample volume = 20 mL
Solution: COD = ((25.0 - 10.5) * 0.25 * 8000) / 20\nCOD = (14.5 * 0.25 * 8000) / 20\nCOD = 29000 / 20 = 1450 mg/L
Result: COD = 1450 mg/L
Example 2: Industrial Effluent with Dilution
Problem: Blank = 22.0 mL, Sample = 18.0 mL, FAS = 0.1 N, Volume = 10 mL, Dilution = 5x
Solution: COD = ((22.0 - 18.0) * 0.1 * 8000) / 10 * 5\nCOD = (4.0 * 0.1 * 8000) / 10 * 5\nCOD = 320 / 10 * 5 = 1600 mg/L
Result: COD = 1600 mg/L
Frequently Asked Questions
What is Chemical Oxygen Demand (COD)?
Chemical Oxygen Demand is a measurement of the amount of oxygen required to chemically oxidize organic and inorganic matter in a water sample using a strong oxidizing agent, typically potassium dichromate. COD is expressed in milligrams of oxygen per liter (mg/L) and is a key indicator of water pollution levels. Higher COD values indicate greater contamination, with typical domestic wastewater having COD values between 250-800 mg/L, while industrial effluents can exceed 10,000 mg/L.
What is chemical equilibrium and Le Chatelier's principle?
Chemical equilibrium occurs when forward and reverse reaction rates are equal. Le Chatelier's principle states that a system at equilibrium will shift to counteract any change. Adding reactant shifts equilibrium toward products. Increasing temperature favors the endothermic direction.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
Can I use the results for professional or academic purposes?
You may use the results for reference and educational purposes. For professional reports, academic papers, or critical decisions, we recommend verifying outputs against peer-reviewed sources or consulting a qualified expert in the relevant field.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.
Why might my result differ from another tool or reference?
Differences typically arise from rounding conventions, the specific version of a formula (for example, simple vs compound interest), or unit inconsistencies between inputs. Check that both tools are using the same formula variant and the same units. The References section links to the authoritative source behind the formula used here.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy