Truss Calculators Hub

It computes the rake length — the sloped length of the roof line at the gable end, from the eave edge to the ridge. Inputs are the building span, the eave overhang, and the pitch as rise-per-12. It also reports the rafter run (half span plus overhang), the pitch angle in degrees, and the slope factor √(1 + (p/12)²) used in rafter-length math, so every number it prints can be reproduced with a framing square.

The Simple Geometric tab is trigonometry for builders: it answers 'how long is the sloped gable edge?' from three framing dimensions. The Structural Analysis tab is mechanics of materials: it solves the internal tension and compression force in every member of a Pratt, Howe, Scissor, or custom truss under your applied joint loads using the direct stiffness method — the same algorithm professional analysis software uses.

Climate and material drive the answer. Shingle manufacturers commonly require at least 2/12 to 3/12; 4/12 to 6/12 is the walkable residential sweet spot; snow country often goes 7/12 and steeper; metal roofing tolerates low slopes. Steeper pitches increase rake length and truss height, which raises material cost — the slope-factor table on this page quantifies exactly how much.

A 2D truss is stable and statically determinate when members + reaction components = 2 × joints (m + r = 2j). The calculator checks this automatically and reports it above the member forces table. Unstable configurations (too few members or supports) produce a singular stiffness matrix, and the tool tells you to check supports and connectivity instead of returning meaningless numbers.

Both US/Imperial and Metric are supported and you can switch at any time — imperial works in feet, kips, in², and ksi, while metric works in meters, kilonewtons, mm², and GPa. All entered values convert automatically, and the calculation report is labeled with the active unit system.

Start with dead load (weight of roofing, sheathing, and framing — often 10–20 psf of roof plan area) plus your local ground snow load as a live load, distributed to the joints the tributary way: top-chord joints typically carry the panel length times the tributary width times the combined pressure. Enter gravity loads as negative Fy values. These are starting-point estimates only — final design loads come from your local building code.

No. The tools are for planning, learning, and pre-design estimation. They analyze idealized pin-jointed trusses and do not select member sizes, design connections, check bracing, or account for your jurisdiction's code amendments. Real trusses must be designed and sealed by a licensed engineer or certified truss manufacturer for the loads, spans, and codes that apply to your project.

Yes — both tabs run entirely in your browser with no sign-up, no limits, and no data sent to a server. The Structural Analysis tab can even encode your whole configuration into a shareable URL, so a saved link reproduces the exact truss, loads, and result on any colleague's machine.

By the standard sign convention, a positive axial force means the member is in tension (being stretched) and a negative value means compression (being squeezed). The truss diagram reinforces the table: tension members are drawn in one color and compression members in another, so the load path through the structure is visible at a glance before you read a single row.

Yes. Both tabs are responsive and touch-friendly — inputs stack vertically on narrow screens, the truss diagram scales to the viewport, and the force table scrolls horizontally rather than truncating. Many users run the geometry tab on a phone at the lumberyard and the analysis tab on a desktop back at the office.

Carpenters and the calculator use the terms interchangeably, but building manuals can be stricter. What framers call a 6/12 pitch — six inches of rise per twelve inches of run — is technically a slope; true pitch is the ratio of rise to the full span, so a 6/12 slope on a 24-ft building is a 1/4 pitch. Because rise-per-12 is what appears on framing squares, speed squares, and rafter tables, this site always states roof angle as rise-per-12 and treats 'pitch' as the everyday word for it. If a plan sheet ever gives you a fraction like 1/3, convert it: slope = rise/run = (1/3) × 2 = 8/12 for a symmetric gable.

Multiply the pressure by the tributary area each joint supports. A joint on the top chord tributes roughly the truss spacing times the horizontal panel length between adjacent joints. Example: 25 psf total load (dead plus snow), trusses at 2 ft on center, and 4 ft between top-chord joints gives 25 × 2 × 4 = 200 lb, or 0.2 kip, entered as Fy = −0.2 at each loaded joint. End joints at walls usually carry half of that because their tributary panel is only on one side. This plan-area shortcut slightly overstates load on steep roofs — precise work converts to along-slope panel lengths first.

A scissor's bottom chord slopes up toward the ridge, so its axial force has a horizontal component that pushes outward on both walls for the entire length of the bearing. A parallel-chord or flat-bottom truss of the same span and load keeps most of that force internal. Run the Scissor preset, then compare its support reaction Rx against the Fink or Parallel Chord presets at identical loads — the difference is immediately visible in the reaction arrows. Real buildings absorb this thrust with raised-heel connections, ridge straps, or a structural ridge, which is why scissor trusses are almost always engineer-sealed rather than field-built.

Spacing does not enter a single-truss analysis directly — it scales how much roof area, and therefore how much load, each truss collects. North American residential framing is typically 24 in on center (16 in for heavy roofing or snow districts), engineered metal-plated trusses commonly run 24 in, and pole-barn trusses often space 4 to 8 ft apart with purlins instead of sheathing. Whatever spacing you build at, use it in the tributary-area math that converts psf pressures into the joint loads you enter — the FAQ above works through that conversion step by step.

Yes — loads are free vectors, so nothing forces you to push down. Wind uplift enters as positive Fy (upward) at the joints it affects, and a net lateral wind pressure on the gable end becomes a row of Fx values along one chord. The solver treats any combination the same way: members that were in compression under gravity may flip into tension, the roller may need to hold down rather than just up, and checking the reaction signs tells you whether connections must resist uplift. Because real wind loading is a code-driven pressure map, treat these runs as directional studies, not certified values.