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Truss Member Force Calculator

Work out truss member force instantly with clear inputs, formula shown and shareable results.

About Truss Member Force Calculator

For a simple triangular truss with load applied at the apex, each support carries half the load. Resolving at the support, the rafter force is the reaction multiplied by the rafter length divided by the rise, and the bottom tie force is the reaction multiplied by the half span divided by the rise. A flatter truss therefore has much larger member forces for the same load.

Formula

Member forces

Rafter = R x rafter length / rise; tie = R x (span/2) / rise, with R = load / 2

Worked example

With the default values below, Truss Member Force Calculator returns Rafter force in compression of 63.25. Change any input above and every figure here is recalculated in your browser.

Inputs used

Truss spanminimum 0.5 m
12 m
Truss rise at apexminimum 0.1 m
2 m
Total load on the trussminimum 0.1 kN
40 kN

Results

Rafter force in compression
63.25 kN
Bottom tie force in tension
60.00 kN
Support reaction
20.00 kN
Rafter length
6.325 m

Step by step

  1. 1Values used
  2. 2Member forces
  3. 3Rafter force in compression= 63.25 kN
  4. 4Bottom tie force in tension= 60.00 kN
  5. 5Support reaction= 20.00 kN
  6. 6Rafter length= 6.325 m

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Preliminary estimate only. Truss analysis and member design must be carried out by a qualified structural engineer including wind uplift, buckling and connection design.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Truss analysis and member design must be carried out by a qualified structural engineer including wind uplift, buckling and connection design.

Frequently Asked Questions

How is the Truss Member Force figure worked out?

Rafter = R x rafter length / rise; tie = R x (span/2) / rise, with R = load / 2. For a simple triangular truss with load applied at the apex, each support carries half the load.

Why do shallow trusses have such large forces?

The rise is the lever arm resisting the applied moment. Halving the rise doubles both chord forces, which is why low-pitch trusses need much heavier chords.

What values do I need to enter?

This calculator takes 3 inputs: Truss span, Truss rise at apex, Total load on the truss. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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