The Law of Definite Proportions vs. The Law of Multiple Proportions

The Law of Definite Proportions (or Proust's Law) states that in a single chemical compound (such as H2O or CO) the ratio of it's component elements is a fixed whole number ratio. For example, in water (H2O) the ratio of hydrogen to oxygen is 2:1 (sometimes written 2/1). In Carbon monoxide (CO) the ratio of carbon to oxygen is 1:1 (or 1/1). Always remember that the law of definite proportions concerns the ratio of elements in a single compound. Here is the example of water visualized.

Law of Definite Proportions Example

This also applies if you use multiples of your original ratio. For example, you could double water's 2:1 hydrogen to carbon ratio. This result's in a 4:2 ratio with two water molecules produced as the end result. This is visualized below.

Law of Definite Proportions Second Example w/ Water

The Law of multiple proportions applies when two or more elements/compounds have multiple ways of combining into different compounds. This is different from the law of definite proportions where we looked at the ratio of elements in a single product, here we are looking at multiple products, as the name of the law implies. When you have a fixed amount of one element (such as carbon (C) or Nitrogen (N)) and you combine it with differing amounts of another element (such as oxygen (O)) the differing amounts of differing amounts of variable element can be expressed as a ratio of whole numbers. For example, the combination of carbon + oxygen forms two simple compounds which illustrate this point. The first is carbon monoxide (CO) and the second is carbon dioxide (CO2). If you start with a fixed 100 grams of carbon and combine it with 133 grams of oxygen, CO will be formed. If on the other hand you combine it with 266 grams of oxygen, CO2 is formed. The ratio of the different amounts of oxygen (266/133) simplifies to a whole number ratio of 2/1. This is the effect which the law of multiple proportions highlights. Another example using nitrogen monoxide and dioxide is illustrated in the example below.

Law of Multiple Proportions Example
  As we can see the ratio of the different oxygen levels (2.286/1.143) is a simple whole number ratio of 2:1 as the law of multiple proportions would have told us.

Thank you for reading! Hopefully you understand the difference between the law of definite proportions and the law of multiple proportions!



  1. This helped so much. I had watched many videos, but this helped the most.

  2. Thanks for the detailed explanation. Can you please help in understanding how the law of multiple proportions proved the existence of atoms?

  3. God thanks so much you truly made my brain happy

  4. I really loved the explanations...I've been looking for this clear differentiation of the two of them because I sometimes confuse them...thanks

  5. This has cleared my all mystery
    Very clear understanding of concept 👍

  6. Nice to be visiting your blog once more, it has been months for me. Well this article that ive been waited for therefore long. i want this article to finish my assignment within the faculty, and it has same topic together with your article. Thanks, nice share. visa pelancongan kanada

  7. keep it up! You have done a great job. Let me tell you about a site where you can find all types of Bollywood and Hollywood movies and serials. moreover, you can also find the best entertainment of Hollywood in Hindi dubbed. You can check the movipapa and search for your favorite movies of all time. Go and explore the ocean of entertainment on the website.


  8. This website was... how do you say it? Relevant!! I finally found something that helped me.The Turkish e visa is an electronic visa Turkey that grants entry into Turkish. Once available, eligible citizens will be able to complete the online application process without having to visit an embassy or consulate.

  9. Superb information article. Thank you . The travelers need to fill up the Kenya visa application form to get the Kenya visa. Therefor, if the apply online, will get the fastest visa services with 24 hours customer support.