Free Online Truss Calculator

The rake is the sloped edge of your roof at the gable end — the distance from the eave edge up to the ridge along the roof line. Knowing it tells you how much siding, trim, fascia, and underlayment the gable ends need, and it is the first number most truss manufacturers ask for when you request a bid. Our Simple Geometric tab computes it from the span, overhang, and pitch in one step.

Pitch expressed as rise-per-12 converts to an angle with atan(rise/12). A 4/12 pitch is 18.4°, 6/12 is 26.6°, and 12/12 is exactly 45°. The Simple Geometric tab shows this angle automatically next to your result, along with the slope factor used for rafter-length math.

The Simple Geometric (DIY/Framing) tab answers framing questions with basic trigonometry: rake length, run, and pitch angle from your building dimensions. The Structural Analysis (Engineering) tab goes further — it solves the internal tension and compression forces in every member of a Pratt, Howe, Scissor, or custom truss using the direct stiffness method, the same approach professional software uses.

In the Structural Analysis tab, positive axial forces are tension — the member is being pulled tight — and negative forces are compression, meaning the member is being squeezed. The diagram colors members blue for tension and red for compression so you can read the load path at a glance.

A truss is statically determinate when the member count plus support reactions equals twice the joint count (m + r = 2j) — its forces can be found from equilibrium alone. Indeterminate trusses (more members than needed) are also solvable here because the stiffness method uses member stiffness; unstable trusses (too few members or supports) are flagged with an error instead of a result.

Typical practice combines dead load (roofing, sheathing, framing weight), live or snow load per your local building code, and wind where applicable — converted to point loads at the joints. Node loads are entered per joint in kips or kilonewtons, and you can load any node in any direction. Always verify design loads against your local code and have final designs checked by a licensed engineer.

A pin fixes a joint in both directions and a roller fixes it vertically only, together providing exactly three reaction components — the minimum needed to prevent any rigid-body movement in 2D. Two pins would over-constrain the truss and hide thermal movement; two rollers would let it slide. The presets set this up automatically at the two ends of the bottom chord.

No. This is a planning and education tool. It analyzes idealized pin-jointed trusses under the loads you enter, but it does not select member sizes, check connections, evaluate bracing, or certify anything for construction. Real trusses must be designed and sealed by a licensed engineer or a certified truss manufacturer for your actual loads, spans, and code jurisdiction.

A zero-force member carries no force under the current load case — the load path simply bypasses it. Three joint patterns identify them by inspection: a joint with two non-collinear members and no load zeroes both; a joint with two collinear members plus a third unloaded member zeroes the third; and a two-member joint loaded along one member zeroes the other. They are not mistakes — under a different load case the same member can carry force, and it braces the chord against buckling. In the Structural Analysis tab, members that solve to roughly zero show up gray, so you can verify these rules against a live result.

Yes. The classic method of joints stalls when m + r exceeds 2j because there are more unknowns than equilibrium equations. The Structural Analysis tab uses the direct stiffness method instead: every member's stiffness is assembled into one global system that is solved for all joint displacements at once, so redundant members are handled naturally. The results header still reports whether your truss is statically determinate, indeterminate, or unstable so you know which case you are in.

A common default for occupied floors is L/360 under live load with L/240 under total load. Stepping up to L/480 (live) and L/360 (total) is typical beneath brittle finishes like tile, stone, or plaster, where cracking matters more than feel. Keep in mind that displacements depend on member cross-sectional area and stiffness, so if you want meaningful deflection numbers from the Structural Analysis tab, set realistic areas and a realistic modulus of elasticity in the advanced panel rather than leaving them at defaults.

In North America the common choices are SPF (Spruce–Pine–Fir), Southern Pine, Douglas Fir-Larch, and Hem-Fir. Species matters because it sets the allowable stresses and the capacity of the metal connector plates — Douglas Fir-Larch and Southern Pine sit at the stronger end, SPF is the widely available workhorse. This calculator computes the axial forces; species and grade enter later, when a designer sizes actual members against those forces.

For most production roofs, trusses win on speed and cost: they arrive factory-built, a small crew sets them in a day or two, and the triangulated geometry spans large rooms without interior bearing walls. Rafters (stick framing) still make sense when you want an open, future-friendly attic or need to improvise around chimneys and odd framing in the field. See the full comparison table in the section above the FAQ.

Start with the rake length: multiply it by your building length to approximate the sheathing area of one roof plane, then add the overhang allowance for soffit and fascia. When you contact a truss manufacturer, have the numbers they will ask for ready — span, pitch, overhang, truss spacing and quantity, and gable-end details. Treat any online estimate as a budgeting aid only: a real quote adds species, plate design, delivery, and crane costs that no estimating tool can see.