Wood Roof Truss Calculator — ft, lumber
How to use this calculator
Enter span, pitch, spacing and building length to calculate gable-roof geometry and the number of truss locations. For lumber and web totals, copy the board feet and member count from the approved truss design drawing or manufacturer quotation; the conceptual King/Queen/Fink/Howe sketch is not a truss design.
Concept profile — the tabs change only the explanatory sketch. Member sizes, webs, joints, connector plates, permanent bracing and reactions must come from the truss design documents.
Geometry — rise and sloped chord length follow the entered span, pitch and horizontal eave overhang.
Saved Calculations
| Time | Type | Span | Pitch | Trusses | Total BF | Cost |
|---|
Wood roof truss geometry and quantity inputs
This page calculates gable-roof geometry and truss locations from the entered span, pitch, horizontal eave overhang, spacing and building length. The King Post, Queen Post, Fink and Howe tabs are conceptual diagrams only. They do not establish member forces, web panel points, lumber grades, connector plates, reactions, permanent bracing or allowable span.
Geometry formulas
Rise = (span / 2) × (pitch / 12). Sloped top-chord reference length = √((span/2)² + rise²) + horizontal eave overhang / cos(θ), where θ = atan(pitch/12). Truss locations = ceil(building length × 12 / spacing in inches) + 1 when the building length is greater than zero. Gable roof area = (span + two horizontal eave overhangs) × building length × √(1 + (pitch/12)²); rake overhang is not included.
Design quantities
Board feet per truss and web-member count are entered from the approved truss design drawing or manufacturer quotation. Total entered board feet = entered board feet per truss × truss locations. Pricing by board foot uses only that entered design quantity; fabricated-truss pricing uses truss count × quoted price per truss.
Required project checks
The truss design must address project loads, load combinations, bearing, reactions, member design, joints and connector plates, deflection, permanent and temporary bracing, handling and installation. Verify the locally adopted building code and the edition of ANSI/TPI 1 referenced by the project. Do not fabricate or alter a metal-plate-connected truss from the conceptual diagram on this page.
Calculation notesWhat this calculator doesOpen the formula basis, references and assumptions when you need to verify the detailed method.Review details
Roof span, pitch, overhang and spacing are converted to truss geometry, member lengths, truss count and preliminary lumber quantity.
Reference context
- • IRC
- • AWC NDS and span-table context
- • manufacturer fastening and product data
Important assumptions
- • Dimensions, quantities and prices entered by the user are correct.
- • Waste, laps, overlaps, compaction and delivery allowances must match the actual project.
- • Results are preliminary takeoff estimates, not a sealed structural design or permit approval.
Quality notes updated: August 1, 2026. The repository includes per-page checks for browser errors, populated results, metadata, US-market visibility, duplicate IDs and shared quality controls.
Reference names describe the applicable design and product context; they do not replace a project-specific code review. Local codes, drawings, specifications and manufacturer instructions govern the final work. Report a calculation or interface issue.
