How to calculate a pipe schedule number

Written by pauline gill
  • Share
  • Tweet
  • Share
  • Pin
  • Email
How to calculate a pipe schedule number
Pipe schedule numbers are based on pipe wall thickness. (steel image by Oleg Guryanov from

The original design process of calculating a suitable pipe schedule number first devised in 1939 has since evolved into selecting an appropriate pipe schedule for an application. The original intent of the Pipe Schedule System was that all pipe diameters within a pipe schedule designation such as Schedule 40 would have the same burst and working pressure ratings. Since then, other factors, such as materials strength and temperature effects, have entered the picture such that designers use validated physical data to select the right pipe schedule for an application.

Skill level:

Things you need

  • Calculator or Spreadsheet

Show MoreHide


  1. 1

    Define the original pipe schedule calculation. The accepted formula is Schedule Number = 1,000 x (P/S) where P = internal pressure, pounds-per-square-inch-gauge (psig) and S = allowable fibre stress (ultimate tensile strength of the steel in psi).

    How to calculate a pipe schedule number
    A good scientific calculator helps pipe calculations immensely. (calculator image by Randy McKown from
  2. 2

    Rearrange terms to solve for P, assuming schedule number and S are known. Therefore P = Schedule number x S/1,000

  3. 3

    Calculate P based on Schedule 40 steel pipe, and an S value of 65,300-psi for mild steel pipe. Therefore, P = 40 x 65,300/1,000 = 2,612-psi. This is reasonable, based on a current-day published value of 2,849-psi for 1-inch Schedule 40 steel pipe.

  1. 1

    Define the pipe application. In this example, 500-psig superheated steam at 316 degrees Celsius needs to flow through a 2-inch nominal diameter steel pipe from a boiler to a turbine. With this information, you can determine the suitable schedule number for this application

  2. 2

    Calculate the maximum allowable pressure rating. According to the American Society of Mechanical Engineers, the actual pressure should be about 25 per cent of the maximum allowable pressure rating. Therefore, 500-psig/0.25 = 2,000-psig.

    How to calculate a pipe schedule number
    Schedule 40 steel pipe in everyday use. (gauge image by from
  3. 3

    Consult the pressure temperature chart to select the appropriate schedule for 2-inch steel pipe. The chart shows a maximum allowable pressure rating at 316 degrees C of only 1,783-psi for 2-inch Schedule 40 pipe, but a rating of 2,575-psig for Schedule 80 pipe. Since the 2,000-psig pressure lies between the two, the Schedule 80 pipe should be selected.

Tips and warnings

  • Check pipe flow restrictions along with other data, as the stronger a particular pipe size gets based on schedule, the smaller is its inner diameter.
  • All designs in which failure of the design or the selected components could result in injury or death should be validated by a professional.

Don't Miss

  • All types
  • Articles
  • Slideshows
  • Videos
  • Most relevant
  • Most popular
  • Most recent

No articles available

No slideshows available

No videos available

By using the site, you consent to the use of cookies. For more information, please see our Cookie policy.