How to Read a Moody Chart (Moody Diagram)

Updated on August 10, 2017

When solving many fluid dynamics problems, be it steady state or transient, the Darcy-Weisbach friction factor, f, is necessary. In circular pipes this factor can be solved directly with the Swamee-Jain equation, as well as others, however most of these equations are complicated, and become cumbersome when iteration is necessary. Therefore, it is often effective to solve for this friction factor using the Moody Chart.



  1. As with many fluid mechanics problems, the first order of business is to determine the Reynolds number of the flow. If you don't have a velocity by which to calculate the Reynolds Number, you will need to assume either a velocity, or a initial friction factor. If you assume an initial velocity, proceed as usual. If you assume a friction factor (I like 0.02), jump to step 10. If done correctly, you will converge at the same answer.
  2. Refer to the Moody Chart. If the Reynolds Number falls in the Laminar or Transition range, refer to appropriate equations. If however the flow is in the Turbulent range, we are ready to proceed with the Moody Chart.
  3. Compute the relative pipe roughness. This value is the roughness of the pipe, divided by the diameter of the pipe. REMEMBER, you want this to be unitless, so ensure that the roughness and diameter are in matching units.
  4. ALSO REMEMBER, just because the wall roughness may be zero, making the relative roughness zero, this does NOT mean that the friction factor will be zero.
  5. Find the line referring to your relative roughness on the right side of the diagram. In the case that your value does not have a printed line, imagine a line paralleling the nearest line representing your relative roughness. It may be helpful to sketch in this line.
  6. Follow this line to the left as it curves up until to reach the vertical line corresponding to your flow's Reynolds Number.
  7. Mark this point on the Chart.
  8. Using a straight edge, follow the point straight left, parallel to the x axis, until you reach the far left side of the chart.
  9. Read off the corresponding friction factor.
  10. Calculate the energy losses knowing the friction factor.
  11. Calculate a new velocity and Reynolds Number.
  12. Compare your new Reynolds Number with your previous value. If the Reynolds number is appreciably different from your previous value, repeat the calculations with this new Reynolds Value. If however it is close to your previous value, your answer has converged, and you are finished.

Quick Example

Let's imagine we calculate a Reynolds Number of 4x10^4 (yes I'm rigging for simplicity). We see that this is in the Reynolds Number range for turbulent flow, so we proceed with the Moody Chart. Next, let's say we calculate a unitless relative roughness of 0.003. From here we sketch a line following the curve contours, going left, as see in the red line below. We follow this line until you Reynolds number value from before, and mark this point. From here, we look straight left, shown by the orange line, until we hit the left margin of the chart. Here we read off our value of 0.03.

At this point, we would compute a new velocity, and a new Reynolds Number, and iterate if necessary.


Other things to be aware of

  • Both the Reynolds number and relative roughness are unitless values when computed correctly, therefore the Moody Chart is unitless, so the same chart applies to US Customary and SI unit systems.
  • Another common mistake when reading the Moody Diagram is improper interpolation between lines and points. Be aware of the logarithmic nature of the axes and labels values, halfway between the values is NOT halfway between the points
  • This system will only work for steady state analysis. If the problem is transient, you can still solve for the end state, however no information can be gleaned from what happens between initial state and steady state. To do this, other methods including numerical analysis, or FEA will be necessary.


    0 of 8192 characters used
    Post Comment
    • profile image

      Raj Kc 

      3 years ago

      For the new velocity we have to use the net head??

      like new assume velocity = (2*g*Hn)^0.5

      Hn =Hg-Hl

      where Hg= Gross head

      Hl = Head loss

    • profile image


      3 years ago

      I wish that all these adds were not littering and obstructing your page.


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
    ClickscoThis is a data management platform studying reader behavior (Privacy Policy)