TRUSS CALCULATOR | SUNSHINE COAST, BRISBANE & SOUTH EAST QUEENSLAND

Truck bed with crane lifting a long wooden beam on a sunny day.

CALCULATE YOUR ROOF TRUSSES EASILY

At Leach Trusses, we’ve been supporting builders and homeowners across the Sunshine Coast since 1978. Whether you’re a DIYer installing a granny flat, an owner-builder creating your dream home, or managing a residential or commercial project, our expertly engineered roof trusses are designed to make construction quicker, easier, and more reliable.


With decades of experience, we know that accurate truss calculations are essential for a safe and cost-effective roof. That’s why we’ve created a simple online truss calculator to help you plan your project confidently.


Call (07) 5494 1077 for guidance or a free consultation — we serve Gympie, Noosa, Maroochydore, Caloundra, Caboolture, Morayfield, North Lakes, Brisbane, and all surrounding areas.

HOW TO CALCULATE RAFTER LENGTH

CALCULATING RAFTER LENGTH USING RISE


  1. Measure your roof span (in metres).
  2. Apply Pythagoras’ theorem:
    a² + b² = c²
  • a = half the roof span
  • b = the rise
  • c = the rafter length

Example (metric):
For a 6 m span with a 2 m rise:

  • Half span = 3 m
  • Rafter length = √(3² + 2²)
    = √(9 + 4)
    = √13
    ≈ 3.6 m


CALCULATING RAFTER LENGTH USING ROOF PITCH (DEGREES)


  1. Measure the horizontal run (half the span).
  2. Use the pitch angle to determine rise:
  • rise = run × tan(angle)
  1. Apply Pythagoras’ theorem to calculate rafter length:
    rafter = √(run² + rise²)

Example (metric):
For a roof with a 6 m span and a 20° pitch:

  • Run = 3 m
  • Rise = 3 × tan(20°) ≈ 1.09 m
  • Rafter = √(3² + 1.09²)
    = √(9 + 1.19)
    = √10.19
    ≈ 3.19 m

CALCULATING THE RISE IF THE RAFTER LENGTH IS KNOWN

If you already know the rafter length and run:
rise = √(c² − a²)

  • c = rafter length
  • a = run


TRUSS CALCULATOR TOOL

We’ve made calculations simple with our interactive truss calculator. Just input your numbers—span, rise, pitch, and overhang — and the tool will instantly give you:

  • Rafter length
  • Roof rise
  • Roof pitch
  • Estimated number of trusses


Whether you’re building a house, shed, granny flat, or commercial roof, this tool ensures you get accurate results without the stress of manual calculations.

right-triangle

Understanding how the maths works helps, but our easy-to-use tool does the hard work for you, saving you time and helping your project stay on track.

OVERVIEW OF ROOFING TERMINOLOGY

Before diving into calculations, it helps to understand the key terms:


  • SPAN – Distance between the outside walls supporting the roof.
  • RUN – Half the span, forming the base of the right-angled triangle used in calculations.
  • RISE – The height of the roof from the top of the wall to the ridge.
  • RAFTER – The angled beam forming the hypotenuse of the triangle.
  • OVERHANG – Extra roof length beyond the walls, typically 450mm–600mm.
  • PITCH – The slope of the roof, often expressed as a degree.


Knowing these terms will make Pythagoras’ theorem and trigonometry calculations much easier.

FAQS

  • CAN I CALCULATE TRUSSES FOR ANY ROOF TYPE?

    Yes. Our calculator works for gable, flat, and pitched roofs — ideal for residential and commercial projects.

  • DO I NEED TO KNOW ADVANCED MATH TO USE THE TOOL?

    Not at all. Simply input the numbers, and the tool calculates the rest using right-angle trigonometry.

  • IS THIS TOOL SUITABLE FOR DIYERS AND PROFESSIONALS?

    Absolutely. Builders, owner-builders, and DIY enthusiasts all use it to plan accurately and save on time and cost.

  • CAN LEACH TRUSSES PROVIDE CUSTOM TRUSSES BASED ON THESE CALCULATIONS?

    Yes. Once you have your measurements, we can design and manufacture custom roof trusses tailored to your project requirements.

WHY CHOOSE LEACH TRUSSES FOR CALCULATING AND SUPPLYING TRUSSES

  • Decades of Expertise – Over 40 years supplying the Sunshine Coast, Brisbane, and SE Queensland.
  • Precision Engineering – Calculations and designs are accurate to ensure safety and compliance.
  • Custom Solutions – Tailored trusses for homes, sheds, commercial buildings, or unusual rooflines.
  • Reliable Support – Guidance from our knowledgeable team to help you plan and execute your project.
  • Fast, Local Service – Designed, manufactured, and delivered efficiently from our Landsborough workshop.

 

Call (07) 5494 1077 or email us today for help with your roof truss calculations or a free quote.

Use our truss calculator today or call (07) 5494 1077 for expert advice.