Chemical Oxygen Demand Calculator
Compare blank and sample titrations to quantify oxygen demand for wastewater and process streams.
Use 1 if the sample was not diluted before digestion.
Chemical oxygen demand
121.6 mg/L
How to Use This Calculator
Run blank and sample titrations
Digest both blank and wastewater samples under the same sealed conditions and record titrant volumes.
Enter titration data
Provide blank volume A, sample volume B, titrant normality, and the sample aliquot volume.
Account for dilution
If the sample was diluted before digestion, multiply the COD by the dilution factor.
Review COD result
Use the calculated COD to gauge organic loading, treatment performance, or permit compliance.
Formula
COD (mg/L) = (A - B) * N * 8000 * dilution / sample volume
A and B in mL, N in equivalents per liter, sample volume in mL. The 8000 constant converts milliequivalents of oxygen to mg/L.
Example
If A = 12.4 mL, B = 4.8 mL, N = 0.10 eq/L, volume = 50 mL, dilution = 1, COD = (12.4 - 4.8) * 0.10 * 8000 / 50 about 152 mg/L.
Full Description
Chemical oxygen demand quantifies the amount of oxidizable material in water by measuring how much dichromate oxidant is consumed during digestion.
The titration difference between blank and sample reflects oxygen used by organic compounds. Converting this difference to mg/L helps operators track treatment efficiency.
Frequently Asked Questions
Why use 8000 in the equation?
Eight thousand converts milliequivalents of oxygen per liter to mg/L when volumes are in mL and normality is in eq/L.
What if the sample requires less titrant than the blank?
That is normal. A lower B value indicates oxygen demand. If B exceeds A, recheck the digestion and titration steps.
Can I use different oxidants?
Dichromate is the standard. Alternative oxidants require different stoichiometry and constants.
How do I report diluted samples?
Multiply the calculated COD by the overall dilution factor to represent the original sample strength.
Does COD equal BOD?
No. COD typically exceeds biochemical oxygen demand because it measures total chemically oxidizable matter, not just biodegradable material.