Introduction
A truss is a structure made of straight members connected at joints to form triangles. Trusses are used in roofs, bridges, and towers because triangles spread out loads in a very strong and efficient way. Engineers need to know the forces in each member of a truss to make sure it can safely carry the weight placed on it. Our Truss Calculator helps you do exactly that.
This tool has two modes. The Quick Roof Truss mode lets you pick a common roof truss type—like Fink, King Post, or Warren—enter your span, pitch, overhang, and spacing, and instantly get key measurements such as peak height, chord lengths, and how many trusses your building needs. The Advanced Analysis mode goes further. You can build any 2D truss by adding nodes, members, loads, and supports, or load a preset like a Pratt bridge or cantilever frame. The calculator then uses the direct stiffness method to solve for member forces, support reactions, node displacements, and stresses. Results are shown in clear tables, color-coded diagrams, and a bar chart so you can quickly see which members are in tension and which are in compression.
Both modes support imperial and metric units, and the advanced mode lets you choose from steel, aluminum, wood, or a custom material. Whether you are a student learning structural analysis, a builder planning a roof, or an engineer checking a design, this truss calculator gives you fast and reliable answers.
How to Use Our Truss Calculator
This calculator has two modes. The Quick Roof Truss mode lets you enter basic roof dimensions to get truss measurements, lumber estimates, and a visual diagram. The Advanced Analysis mode lets you build a custom truss and solve for internal forces, stresses, support reactions, and displacements.
Quick Roof Truss Mode
Units: Choose between Imperial (feet and inches) or Metric (meters and centimeters). The calculator will convert all values and results to match your selection.
Truss Type: Pick the shape of your roof truss from the visual grid. Options include Common/Fink, King Post, Queen Post, Scissor, Attic, Gambrel, Pratt, Howe, Warren, and Modified Queen. Each type has a different web pattern that affects material use.
Span / Width: Enter the horizontal distance from one bearing wall to the other. This is the full width your truss must cover. If you need to figure out the total area of your building footprint, our Square Footage Calculator can help.
Roof Pitch: Set your roof slope using either a rise-over-run ratio (like 6/12) or a degree angle. The calculator shows the matching value in the other format so you can confirm it is correct. For a dedicated tool focused entirely on pitch, see our Roof Pitch Calculator.
Overhang: Enter how far the roof extends past the bearing wall on each side. This adds length to the top chord of your truss.
Heel Height: Enter the vertical height at the bearing point where the truss sits on the wall. This is measured in inches or millimeters.
Building Length: Enter the total length of your building along the ridge line. The calculator uses this with the on-center spacing to figure out how many trusses you need.
On-Center Spacing: Select or type the distance between each truss. Common choices are 12, 16, 19.2, or 24 inches. You can also enter a custom value.
Press Calculate to see peak height, top and bottom chord lengths, pitch angle, total truss count, estimated lumber needed, and a scaled truss diagram. Press Reset to return all inputs to their default values.
Advanced Analysis Mode
Units: Choose Imperial (feet and kips) or Metric (meters and kilonewtons). All force, stress, and length labels update to match.
Material: Select Steel, Aluminum, Wood, or Custom. Each material sets the modulus of elasticity (E) used in the stiffness calculations. If you choose Custom, type in your own E value.
Cross-Section Area (A): Enter the cross-sectional area shared by all members. This value is used along with the modulus of elasticity to compute stiffness, forces, and stresses.
Load Preset or Build Custom: Click a preset button to load a ready-made truss such as a Simple Bridge, Warren, Pratt, Howe, Roof Fink, or Cantilever. This fills in all nodes, members, loads, and supports for you. You can also build your own from scratch.
Nodes: Add points that define the joints of your truss. Each node needs an X and Y coordinate. You can edit or delete nodes in the table below the diagram.
Members: Add bars that connect two nodes. Pick the start and end node for each member. The calculator shows the length automatically.
External Loads: Add forces at any node. Enter a horizontal force (Fx) and a vertical force (Fy). Use negative Fy values for downward loads. If you need to understand force fundamentals, our Force Calculator is a helpful companion tool.
Supports: Add boundary conditions at any node. Choose Pin (blocks horizontal and vertical movement), Roller (blocks only vertical movement), or Fixed (blocks all movement).
Press Analyze Structure to run the finite element solver. The results show each member's internal force labeled as Tension, Compression, or Zero, along with stress values, support reactions, node displacements, a color-coded force diagram, and a bar chart summarizing all member forces.
What Is a Truss?
A truss is a structure made of straight bars or beams connected at joints called nodes. These bars form triangles, which makes the whole structure very strong and stiff. Trusses are used in roofs, bridges, towers, and many other buildings because they can hold heavy loads while using less material than a solid beam.
How Trusses Work
Each bar in a truss carries force in one of two ways: tension (being pulled apart) or compression (being pushed together). When a load like snow, wind, or the weight of a roof pushes down on a truss, the triangle shapes spread that force through every member. This is why triangles are so important in engineering — a triangle cannot change shape without bending or breaking one of its sides, making it the most stable simple shape. You can explore how forces and accelerations interact with our Torque Calculator and Momentum Calculator.
Common Roof Truss Types
Roof trusses come in many styles, and each one is suited for different situations:
- Fink (Common) Truss — The most popular type for homes. Its web members form a "W" pattern that efficiently handles typical residential roof loads.
- King Post Truss — The simplest truss with a single vertical bar in the center. Best for short spans up to about 20 feet.
- Queen Post Truss — Uses two vertical bars instead of one, allowing for wider spans than a king post.
- Scissor Truss — The bottom chord slopes upward toward the center, creating a vaulted ceiling inside the building.
- Attic Truss — Designed with a rectangular open space in the middle so you can use the attic as a room.
- Gambrel Truss — Has a double-slope shape like a barn roof, giving extra headroom in the upper level.
- Pratt, Howe, and Warren Trusses — Commonly used in bridges and flat-roofed buildings. They differ in the direction their diagonal members lean, which changes whether those diagonals carry tension or compression.
Key Truss Measurements
When designing a truss, several measurements matter:
- Span — The horizontal distance from one bearing wall to the other. This is the main gap the truss must bridge.
- Roof Pitch — The steepness of the roof, usually written as a ratio like 6/12, meaning the roof rises 6 inches for every 12 inches of horizontal run. Steeper pitches shed rain and snow better but use more material. Our Roof Pitch Calculator can help you convert between pitch ratios and degree angles.
- Overhang — How far the roof extends past the walls. Overhangs protect walls from rain and provide shade.
- Heel Height — The vertical distance at the point where the truss sits on the wall. A taller heel gives more room for insulation. For planning your insulation needs, try our Insulation Calculator.
- On-Center Spacing — The distance between each truss along the length of the building. Common spacings are 24 inches for residential and 16 inches for heavier loads.
Structural Analysis: The Method of Joints
Engineers figure out the force in every bar of a truss using a method called structural analysis. The most common approach for simple trusses is the direct stiffness method, which uses math to solve for how much each joint moves and how much force each bar carries. Every truss must be in equilibrium, meaning all forces must balance out so the structure stays still. The supports (pins and rollers) provide reaction forces that push back against the applied loads. For related structural calculations, our Beam Deflection Calculator helps you analyze bending in individual beams, and the Moment of Inertia Calculator is useful when evaluating cross-section properties.
Tension vs. Compression
A member in tension is being stretched. Tension members can be thin because pulling on a bar does not cause it to buckle. A member in compression is being squeezed. Compressed bars need to be thicker because a thin bar under compression can suddenly buckle and fail. Knowing which members are in tension and which are in compression helps engineers choose the right size and material for each part of the truss. Understanding stress and strain is closely related to concepts like spring force and material stiffness.
Why Truss Calculations Matter
Getting truss calculations right is essential for safety. An undersized truss can sag, crack, or collapse under heavy loads like accumulated snow or strong winds. An oversized truss wastes material and money. Accurate calculations help builders use just the right amount of lumber or steel, keeping the structure safe and the cost down. When planning the rest of your roof, you may also find our Rafter Calculator, Roof Area Calculator, and Shingle Calculator useful. If your project involves framing walls to support those trusses, check out our Framing Calculator and Stud Calculator. For estimating lumber in board feet, our Board Foot Calculator can help with material purchasing. For any real building project, a licensed structural engineer should review and approve all truss designs before construction begins.