Omni calculator
Last updated:

Chemical Oxygen Demand Calculator

Table of contents

What is chemical oxygen demand?How to use the chemical oxygen demand calculatorDifference between BOD and CODChemical oxygen demand formulaSignificance of determining chemical oxygen demandFAQs

Life feels good when you come across essential tools, especially if the tool is a chemical oxygen demand calculator. This would definitely be good news for all the chemistry enthusiasts and students out there.

But wait, even if you are not a chemistry nerd, it would still benefit you to know:

  • What is chemical oxygen demand;
  • How to determine chemical oxygen demand?; or the
  • Difference between biochemical oxygen demand (BOD) and COD — chemical oxygen demand.

But we won't stop there. In this article, we will also discuss the significance of determining the chemical oxygen demand, which can come in handy in understanding the quality of water based on the presence of organic pollutants. So, what are you waiting for? Let's dive in and soak in some knowledge.

What is chemical oxygen demand?

Chemical oxygen demand, or COD, measures the capacity of water to consume oxygen during the decomposition of organic matter in the water. In other words, it's the amount of oxygen needed to oxidize the organic matter present in a quantity of water.

The unit of COD is milligrams per liter (mg/L), which indicates how much oxygen is consumed per liter of a solution.

The concentrations of COD estimate the amount of organics in the water. A low COD means that the water is safer or has fewer pollutants. In comparison, a higher COD is an indication of extreme pollutants. In a situation where your COD test yields a negative value, there was some error in the test, and it needs to be rerun.

Whether you're a scientist or an environmental warrior, knowing the COD can help you understand just how clean (or dirty) a body of water 💧 really is.

How to use the chemical oxygen demand calculator

COD tells us how thirsty the water is for oxygen, especially when there's a bunch of organic gunk floating around that needs to be broken down.

The tools that help you assist in chemistry-related problems could not get any simpler than our chemical oxygen demand calculator.

Using the chemical oxygen demand calculator requires only a few simple steps. Just take them one by one, and you will have your required result.

  1. The first thing you need to input is the volume of ferrous ammonium sulfate (FAS) for the blank run.

  2. Next, input the volume of FAS for the sample.

  3. After that, input the normality of FAS.

  4. Lastly, you need to input the volume of the original sample for which you are testing the chemical oxygen demand. The unit of all the volume measurements is milliliters (ml).

  5. The result will be displayed before you can say "chemical oxygen demand" out loud. The unit of the COD is milligrams per liter (mg/L).

We do have a handy water hardness calculator; you might want to take a look!

Difference between BOD and COD

Biochemical oxygen demand (BOD) sounds slightly different from COD. And that is exactly what they are, slightly different from each other.

They both give us the amount of oxygen that disintegrates the organic pollutants in water. But they differ in a tiny aspect, that is, how does this disintegration take place?

BOD is the amount of oxygen microorganisms require to break down organic materials. Whereas COD is the amount of oxygen to break down the organic material by oxidation.

Chemical oxygen demand formula

COD tests help us evaluate the amount of organic pollutants in water. So, it is somewhat crucial to know the equation behind said tests.

The chemical oxygen demand formula is:

COD=(AB)×N×8000Sample volume\text {COD} = \frac {(A - B) \times N \times 8000}{\text {Sample volume}}


  • COD\text {COD} — Chemical oxygen demand;
  • AA — Volume of ferrous ammonium sulfate for the blank run;
  • BB — Volume of ferrous ammonium sulfate for the sample; and
  • NN — The normality of ferrous ammonium sulfate.

This chemical oxygen demand formula is the basis for the calculations in the COD calculator.

On a side note, we do have a normality calculator, in case you are interested to know more about it. Check it out!

Let's consider an example to answer your question of "how to determine chemical oxygen demand?"

Say you have the data as follows:

COD=(300129)×3×800045000\text {COD} = \frac {(300 - 129) \times 3 \times 8000}{45000}

So, to determine the COD, take it one step at a time until you reach the end.

COD=171×3×800045000=513×800045000=4, ⁣104, ⁣00045000=91.2 mg/L\begin{split} \text {COD} &= \frac {171 \times 3 \times 8000}{45000}\\[1em] &= \frac {513 \times 8000}{45000}\\[1em] &= \frac {4,\!104,\!000}{45000}\\[1em] &=91.2 \text { mg/L} \end{split}

✅ Just a heads-up 📌

COD tells us there are organic pollutants, but it won't spill the beans on what those pollutants are.

Significance of determining chemical oxygen demand

Now, we'll take a look at what is the big deal about COD.

  • Keeping tabs on water quality 🌊
    First off, COD is like the Sherlock Holmes of water quality! It's super crucial for figuring out how many organic nasties are lurking in our water.

  • Wastewater treatment all-stars 🏆
    Monitoring COD levels before and after treating wastewater is like looking at a "before and after" home renovation photo. You get to make sure the treatment methods are doing their job.

  • Keeping industries in check 🏭
    Industries, the double-edged swords of modern life! COD helps us keep tabs on what they're pouring into our waterways. If the COD is too high, they might just have to rethink their wastewater treatment game plan to stay on the right side of the law.

  • A lifeline for aquatic life 🐠
    High COD levels can sound the alarm for low oxygen levels, which is bad news for fish and other aquatic buddies. So, keeping an eye on COD levels helps us make sure our underwater friends can breathe easily.

COD might seem like just a bunch of science jargon, but it's a crucial part of how we understand and protect our precious water resources.

In case you would like to determine or study the total dissolved solids in water, we recommend our TDS calculator.


How can I determine chemical oxygen demand (COD)?

Determining the COD of water is straightforward as long as you have complete data.

  1. Subtract the volume of ferrous ammonium sulfate for the sample from the volume of FAS for blank.
  2. Multiply the result by the normality of FAS.
  3. Multiply the result by 8000.
  4. Lastly, divide the result from Step 3 by the original sample volume.
  5. You have your result, the chemical oxygen demand (COD), in mg/L (if all the volumes are in milliliters).

What does chemical oxygen demand indicate?

Chemical oxygen demand (COD) indicates the presence of organic pollutants in water.

High COD water may contain high levels of impurities like decaying vegetation and human or industrial waste. Whereas water with lower levels of COD may be safe for drinking and other household uses. But remember, it in no way guarantees that low COD water is safe or completely free from health hazards.

How is chemical oxygen demand measured?

You can easily determine the chemical oxygen demand of water using the formula:

COD = ((A - B) × N × 8000) / Sample volume


  • COD — Chemical oxygen demand;
  • A — Volume of ferrous ammonium sulfate for the blank run;
  • B — Volume of ferrous ammonium sulfate for the sample; and
  • N — The normality of ferrous ammonium sulfate.

This formula is the basis for our chemical oxygen demand calculator.

What is a good COD level for drinking water?

The preferred chemical oxygen demand (COD) for drinking water is 10-20 mg/L (milligrams per liter).

Low COD levels signify the suitability of water in terms of safety and palatability. Nonetheless, it is noteworthy that COD levels do not indicate health risks, and many other parameters are involved in declaring water fit for drinking.

Check out 7 similar organic chemistry calculators 🛢️
Combustion analysisCombustion reactionCrude protein...4 more