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🌊 COD / BOD Calculator

Calculate Chemical Oxygen Demand (COD) from dichromate titration data, or Biological Oxygen Demand (BOD₅) from dissolved oxygen depletion.

Mode:

Blank Titrant Volume mL

Sample Titrant Volume mL

FAS Molarity mol/L

Sample Volume Used mL

COD

— mg/L

💡 Note: COD (dichromate method) measures total chemically oxidizable material and typically gives a higher value than BOD, which measures only what's biodegradable within the test period (usually 5 days). BOD without seed correction (as calculated here) assumes the dilution water itself contributes negligible oxygen demand — for seeded dilution water, a seed correction term should be subtracted.

📖 Example (COD): Blank=12.5 mL, Sample=8.2 mL, FAS=0.1 M, sample size=20 mL: COD = (12.5−8.2)×0.1×8000/20 = 172 mg/L. Example (BOD₅): Initial DO=8.6, Final DO=4.2, dilution factor=5: BOD₅ = (8.6−4.2)×5 = 22.0 mg/L.

Frequently asked questions

What's the difference between COD and BOD?

COD (chemical oxygen demand) measures the total amount of oxygen needed to chemically oxidize all organic and some inorganic material in a sample using a strong oxidizer (dichromate), giving a result within hours. BOD (biological oxygen demand) measures only the oxygen consumed by microorganisms biodegrading organic matter over a set incubation period (typically 5 days), and is generally lower than COD since not all chemically oxidizable material is biodegradable.

Why does the COD formula use the constant 8000?

8000 comes from combining the equivalent weight of oxygen (8 g/equivalent) with the conversion from mL to L (a factor of 1000), giving the constant that converts titrant volume x molarity directly into mg/L of oxygen demand.

Does this BOD calculation include seed correction?

No — this is the basic BOD calculation assuming dilution water contributes negligible oxygen demand on its own. If seeded dilution water is used (common when the sample lacks sufficient microorganisms), a seed correction term based on a separate seed blank's DO depletion should be subtracted, which this simplified calculator does not include.

Accuracy & how this is derived

Derivation: COD uses the standard closed reflux/open reflux dichromate titration formula, converting the difference between blank and sample titrant volumes into mg/L oxygen demand via the FAS molarity and the equivalent weight of oxygen. BOD5 uses the standard dissolved oxygen depletion formula, scaled by the dilution factor used in the test.

Validated against: Standard Methods for the Examination of Water and Wastewater (APHA), Standard Method 5220 (COD) and 5210 (BOD) — the standard reference protocols for both measurements.

⚠️ For educational and research support only — verify critical results independently before use in regulated, clinical, or publication-bound work.

✔ Last updated: July 2026 · Report an error

Measuring oxygen demand in water quality analysis

Chemical oxygen demand and biological oxygen demand are both standard measures of organic pollution in water samples, quantifying how much oxygen would be consumed as that organic material is oxidized or biodegraded. COD is determined by a rapid dichromate titration that chemically oxidizes essentially all organic matter present, while BOD measures the oxygen actually consumed by living microorganisms over a fixed incubation period, making COD generally faster to obtain and BOD generally more representative of a water body's real biological oxygen burden.