Purlin Size Calculator


The Purlin Size Calculator is a valuable tool for construction professionals and enthusiasts aiming to determine the optimal purlin size for their projects. Whether dealing with a uniform load or a point load, this calculator provides a quick and precise recommendation based on the entered span length and load type.


The calculator employs distinct formulas for uniform loads and point loads to calculate the recommended purlin size. For a uniform load, the formula involves the square root of the load multiplied by the fourth power of the span length divided by 384. For a point load, the formula utilizes the cube root of the load multiplied by the third power of the span length divided by 48.

How to Use

  1. Enter the span length in feet.
  2. Select the load type (Uniform Load or Point Load) from the dropdown.
  3. Enter the load value in pounds.
  4. Click the “Calculate” button.
  5. View the recommended purlin size in inches in the result.


For instance, if you have a project with a span length of 10 feet, a uniform load, and a load value of 500 pounds, input these values, click “Calculate,” and the calculator will provide the recommended purlin size.


Q1: What is the difference between uniform load and point load? A1: A uniform load is evenly distributed along the entire span, while a point load is concentrated at a specific point.

Q2: Can the calculator be used for different construction materials? A2: Yes, the calculator provides a general recommendation applicable to various materials based on load and span.

Q3: Is the recommended purlin size suitable for all construction projects? A3: The recommendation is a guideline; consult with a structural engineer for specific project requirements.

Q4: How often should I reassess the purlin size recommendation? A4: Reassess when there are changes in project specifications or during key project milestones.

Q5: Does the calculator consider other factors like wind load or snow load? A5: The calculator focuses on span length and load type; consult with an engineer for comprehensive load analysis.

Q6: Can the calculator be used for both residential and commercial projects? A6: Yes, the calculator is versatile and applicable to a range of construction projects.

Q7: What are the units for the recommended purlin size? A7: The result is provided in inches.

Q8: Are there limitations to the calculator’s recommendations? A8: The calculator provides a basic guideline and may not cover all project-specific variables.

Q9: How critical is the selection of the correct purlin size in construction? A9: Purlin size is crucial for structural integrity; selecting the right size ensures the safety and stability of the construction.

Q10: Can the calculator be used for retrofitting existing structures? A10: The calculator is designed for new construction projects; retrofitting may require a more detailed analysis.


The Purlin Size Calculator simplifies the process of determining the appropriate purlin size for construction projects. By considering span length and load type, this calculator provides a valuable starting point for construction professionals and enthusiasts. However, it is essential to collaborate with structural engineers to ensure that the final purlin size aligns with the specific requirements of the project for optimal safety and performance.

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