Introduction
A truss is a structure made of straight bars connected at joints, or nodes, to form triangles. Trusses are used in roofs, bridges, and towers because triangles are very strong and stable shapes. Engineers rely on truss calculations to figure out how much force each bar carries, whether it is being pulled apart (tension) or pushed together (compression), and how the whole structure reacts to loads like snow, wind, or the weight of the roof itself.
This Truss Calculator gives you two powerful tools in one. The Roof Truss Estimator lets you pick a truss style—such as Common/Fink, Howe, Pratt, or Warren—then enter your span width, roof pitch, building length, and truss spacing. It calculates the number of trusses you need, the ridge height, rafter lengths, total roof area, lumber quantities for top chords, bottom chords, and web members, and an estimated lumber cost. The Structural Analysis mode goes deeper. You can define nodes, connect them with members, apply loads at any joint, and solve the truss using the direct stiffness method. It returns support reactions, axial forces in every member, and nodal displacements, all shown in a color-coded force diagram. You can switch between imperial and metric units, choose from preset truss configurations like a simple triangle or a four-panel Pratt truss, and view results in clear tables and charts.
How to Use Our Truss Calculator
This truss calculator has two modes: a Roof Truss Estimator for planning roof builds and a Structural Analysis tool for solving member forces in any truss. Enter your truss dimensions, loads, and material details to get results like lumber totals, costs, member forces, and support reactions.
Roof Truss Estimator
Units: Choose between Imperial (feet, pounds) or Metric (meters, kilonewtons) using the toggle at the top. The calculator will convert all values when you switch.
Language: Pick your preferred language from the dropdown menu. The calculator supports 12 languages including English, Spanish, French, German, and more.
Truss Type: Click on one of the seven truss styles — Common/Fink, Howe, Pratt, Warren, Scissors, Attic, or Simple Triangle. Each type has a different web pattern that affects lumber needs and load paths.
Span Width: Enter the total horizontal distance from one wall to the other. This is the full width your truss must cover. You can verify your wall-to-wall measurement using a Square Footage Calculator to ensure your building dimensions are correct.
Pitch Input Method: Choose either Rise/12 (such as 6/12) or Degrees to set how steep your roof is. A standard home roof is usually between 4/12 and 9/12 pitch. For detailed pitch calculations, our Roof Pitch Calculator can help you determine the exact slope of your roof.
Eave Overhang: Enter how far the roof extends past the wall on each side. This is the part of the roof that hangs over to protect the walls from rain.
Building Length: Enter the total length of the building. The calculator uses this along with truss spacing to figure out how many trusses you need.
Truss Spacing (O.C.): Enter the on-center distance between each truss. A common spacing is 24 inches or 610 millimeters. Our Stud Calculator uses similar on-center spacing concepts for wall framing.
Total Roof Load: Enter the combined dead load and live load your roof must hold. This includes the weight of roofing materials, insulation, and snow or wind loads. A typical value is 30 to 50 pounds per square foot.
Top Chord Lumber: Select the lumber size for the top chord (the sloped piece that runs from the wall to the ridge). Larger spans and heavier loads need bigger lumber like 2×8 or 2×10. You can estimate your lumber needs in board feet using a Board Foot Calculator.
Bottom Chord Lumber: Select the lumber size for the bottom chord (the flat piece that runs along the bottom of the truss between the two walls).
Web Members Lumber: Select the lumber size for the web members (the inner pieces that connect the top and bottom chords in a zigzag or vertical pattern).
Lumber Cost: Enter the price you pay per linear foot or meter of lumber. The calculator uses this to estimate the total material cost for all trusses. To measure lumber in linear feet, our Linear Feet Calculator can assist.
Click Calculate to see the number of trusses, ridge height, rafter length, total roof area, lumber totals for each part, estimated cost, load per truss, and reaction forces. Charts will also show the lumber breakdown and cost split by component.
Structural Analysis
Preset Configurations: Click a preset button — Simple Triangle, Warren, Pratt, Howe, or Cantilever — to load a ready-made truss with nodes, members, and loads already filled in. This is a fast way to get started or to learn how the tool works.
Nodes (Joints): Add each joint in your truss by clicking "Add Node." For each node, enter its X and Y coordinates and pick a support type: Free (no support), Pin (fixed in both directions), or Roller (fixed only in the vertical direction).
Members (Bars): Add each bar by clicking "Add Member." For each member, pick the start node and end node it connects, then enter the cross-sectional area (in square inches or square centimeters) and the modulus of elasticity (in ksi or GPa). For steel, use 29,000 ksi or 200 GPa. For wood, use about 1,500 ksi or 10 GPa.
Applied Loads: Add forces by clicking "Add Load." For each load, pick the node where the force acts, then enter the horizontal force (Fx) and vertical force (Fy). Use negative Fy values for downward loads. If you need to convert load units, our Force Calculator can help.
Click Solve Truss to run the stiffness method analysis. The calculator will display a color-coded diagram showing tension members in green and compression members in red, a table of support reactions, a table of each member's internal force and whether it is in tension or compression, and a table of how much each node moves under the applied loads.
What Is a Truss?
A truss is a structure made of straight bars or beams connected at points called joints or nodes. These bars form triangles, which makes the whole structure very strong and stiff. Trusses are used to support roofs, bridges, towers, and many other things where you need to span a long distance without putting columns or walls in the middle.
How Trusses Work
Trusses work by spreading out a load through their members. When weight pushes down on a truss, some bars get pulled apart (this is called tension) and some bars get squeezed together (this is called compression). The triangle shape is key because a triangle cannot change its shape without bending or breaking one of its sides. This is what makes trusses so much stronger than a single beam of the same weight. For a deeper look at how beams respond to loads, you can explore our Beam Deflection Calculator, which analyzes bending and deflection in single-span beams.
Common Truss Types
There are many styles of trusses, and each one is suited for different jobs:
- Fink (Common) Truss – The most popular roof truss for homes. Its web members form a "W" pattern that handles typical roof loads well.
- King Post Truss – The simplest truss design, with one vertical bar in the center. It works best for short spans.
- Queen Post Truss – Has two vertical bars instead of one, allowing it to cover wider spans than a king post.
- Scissor Truss – The bottom chord slopes upward toward the center, creating a vaulted or cathedral ceiling inside the building.
- Attic Truss – Designed with an open space in the middle so you can use the area inside the truss as a room or storage.
- Gambrel Truss – Has a double-slope shape on each side, like a barn roof. It gives extra headroom in the upper floor.
- Pratt Truss – A flat (parallel-chord) truss where the diagonal members angle toward the center. It is common in bridges and steel buildings.
- Howe Truss – Similar to a Pratt but with diagonals angled the opposite way. It was widely used in early wooden bridges.
- Warren Truss – Uses diagonal members that alternate direction without vertical bars, forming a zigzag pattern. It is efficient and simple to build.
Key Truss Measurements
When you design or buy a roof truss, a few measurements matter most:
- Span – The horizontal distance from one bearing wall to the other. This is the gap the truss must cross.
- Pitch (Rise/Run) – How steep the roof is. A pitch of 6/12 means the roof rises 6 inches for every 12 inches of horizontal run. Steeper pitches shed rain and snow better but use more material. Use our Roof Pitch Calculator or Rafter Calculator to work out these dimensions precisely.
- Overhang – The part of the top chord that sticks out past the wall. It protects the siding and foundation from rain.
- Heel Height – The vertical height of the truss right above the bearing wall. A taller heel lets you fit more insulation at the eaves. Our Insulation Calculator can help you determine how much insulation to install in that space.
- On-Center Spacing – How far apart trusses are placed along the length of the building. Common spacings are 16 inches and 24 inches. This same concept applies when using our Framing Calculator to plan wall and floor framing.
Understanding Truss Analysis
Engineers use a method called the Direct Stiffness Method (a type of finite element analysis) to figure out the forces in each member of a truss. The process works like this:
- Define every node's position, every member's connections, every applied load, and every support.
- Build a mathematical model (a stiffness matrix) that describes how each bar resists stretching or squeezing. Solving this system involves linear algebra similar to what our Matrix Calculator handles.
- Solve the system of equations to find how much each node moves (displacement).
- Use those displacements to calculate the internal force in every member and the reaction forces at the supports.
A member in tension is being pulled apart and could fail by tearing. A member in compression is being pushed together and could fail by buckling. Knowing which members are in tension and which are in compression helps engineers pick the right size and material for each bar.
Material and Cross-Section
Two properties control how stiff a truss member is: the modulus of elasticity (E) of the material and the cross-sectional area (A) of the bar. Steel has a high E value (about 29,000 ksi or 200 GPa), so it deflects less under load. Wood has a much lower E (about 1,700 ksi or 12 GPa), which means wooden trusses need larger members to achieve the same stiffness. Aluminum falls in between. A larger cross-section area also makes a member stiffer and stronger. When working with steel connections, our Bolt Torque Calculator can help you properly specify bolted joints at truss gusset plates.
Supports: Pins, Rollers, and Fixed
Every truss needs supports to hold it in place. The three common types are:
- Pin support – Prevents movement in both horizontal and vertical directions but allows the truss to rotate at that point.
- Roller support – Prevents vertical movement only. The truss can slide sideways and rotate. This is important because it lets the truss expand and contract with temperature changes. You can estimate thermal expansion effects using our Thermal Expansion Calculator.
- Fixed support – Prevents all movement and rotation. It provides the most restraint.
A simple truss typically uses one pin and one roller. This gives enough restraint to keep the truss in place while allowing it to respond naturally to loads.
Important Reminders
This calculator gives estimates for educational and planning purposes. Real-world truss design must account for building codes, snow loads, wind loads, seismic forces, connection details, and wood or steel grades. Always have a licensed structural engineer review and stamp truss designs before they are built. If you are planning a full roofing project, you may also find our Roof Area Calculator, Shingle Calculator, and Decking Calculator helpful for estimating other materials. For foundation work that supports your trusses, consider using the Concrete Calculator and Rebar Calculator to plan footings and piers.