TryBuildCalcRoof Truss Spacing Calculator (16"/19.2"/24" O.C.)
Find your truss count by spacing instantly.
🕒 Last updated: September 4, 2026
Inputs
ℹ️Informational/geometric only — the actual web layout is engineered by the truss designer regardless of the type selected here. Mono is a single-slope truss with no ridge.
ℹ️Outside wall to outside wall — trusses clear-span the full width, unlike stick-framed rafters.
ℹ️The length running along the ridge — determines the truss count.
ℹ️Rise per 12 inches of run — a 6/12 roof rises 6 inches for every 12 inches of horizontal run.
ℹ️Horizontal projection of the truss tail past the outer wall face, before any fascia trim.
ℹ️A raised (energy) heel gives full-depth insulation clearance at the wall line, common in modern energy-code-driven construction.
Waste
ℹ️Accounts for damaged pieces and layout adjustments on common trusses — 10% is a common estimating default.
Cost
Total Trusses Needed
23
21 common (+10% waste) + 2 gable end
Overall Truss Height
6.25 ft
75" from bearing to ridge peak
Truss Geometry
Type: fink
Pitch: 5/12 (22.62° from horizontal)
Run: 180" (15.00 ft)
Rise: 75" (6.25 ft)
Top chord length: 195"
Overhang tail: 13" (12" horizontal overhang)
Overall height (bearing to ridge): 75"
Truss Count
Spacing: 24" O.C. over 36 ft
Common trusses before waste: 19
Total with 10% waste: 21
Gable End Trusses
Count: 2 (one per gable end)
Typically a vertical-stud or step-down "ladder" truss, not the same web pattern as common trusses.
Truss-to-Wall Connectors
Count: 42
One hurricane tie/truss anchor per bearing point (2 per common truss) — confirm rating against local wind/seismic requirements.
Assumptions Used
Standard US light-frame prefabricated wood roof trusses, clear-spanning the full building width. Truss count uses the same on-center spacing formula as wall studs, rafters, and floor joists. Geometry (run, rise, chord length, overhang, overall height) is direct trigonometry from your entered span and pitch — not a code-table lookup, so it applies regardless of code edition. This calculator does not design trusses — real trusses are engineered components with member sizes, web layout, and metal connector plates sized by a truss designer using manufacturer design software, then fabricated to a stamped drawing; this is a quantity and geometry takeoff only. Gable end trusses (when included) are a fixed count of 2, not subject to the waste factor. Truss-to-wall connector count assumes 2 bearing points per common truss and does not include gable end truss fastening (typically toe-nailed/strapped along the gable wall, not a fixed per-truss count). Permanent and temporary bracing — one of the most safety-critical parts of truss installation — must follow the truss designer's own drawings and the industry-standard BCSI guide (SBCA/TPI), not this calculator.
Bill of Materials
Main material: 21 pcs + recommended tools
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Bill of Materials
Main material: 21 pcs + recommended tools
Computed items reflect your entered span, length, and spacing; consumables below are general recommendations — actual needs vary by product, wind/seismic zone, and site conditions.
For Your Job
Roof Trusses
Gable End Trusses
Truss-to-Wall Connectors
General Tools & Consumables
Truss-to-wall connectors (hurricane ties/anchors)
Permanent bracing lumber
Temporary erection bracing lumber
Gable end L-brackets/stiffeners
Roof sheathing (OSB/plywood)
Framing nailer or hammer
Crane or forklift (for lifting trusses into place)
Tape measure
Chalk line
4 ft level
Safety harness & fall protection
Diagram simplified for clarity (not to scale) — actual web layout is set by the truss designer's engineered drawing.
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Roof Truss Calculator.
Truss count by spacing
Truss spacing (16, 19.2, or 24 inches on-center) directly determines how many trusses a given building length needs, using the same even-spacing formula as wall studs and floor joists — 24" O.C. is the most common spacing for engineered trusses.
This page defaults to standard 24" O.C. spacing on a 36 ft building length — edit the inputs above to match your actual roof.
Roof Truss Calculator Formula: How Is It Determined?
Truss geometry, truss count, gable end trusses, and connector hardware, calculated separately and combined into a material takeoff.
Step 1 — Truss Geometry
Run = Common/Scissor/Attic: Span ÷ 2 | Mono: full Span
Angle = arctan(Top Pitch ÷ 12)
Rise = Run × (Top Pitch ÷ 12)
Top Chord Length = Run ÷ cos(Angle)
Overall Height = Heel Height + Rise
This is direct trigonometry applied to your entered span and pitch — a Pythagorean relationship between run and rise, not a code-table lookup, so it applies regardless of code edition. For a scissor truss, the same formula is applied a second time using the bottom chord pitch, and the difference in rise gives the vaulted ceiling height.
Step 2 — Truss Count & Gable Ends
Common Trusses (before waste) = ceil((Building Length in inches) ÷ Spacing) + 1
Total Common Trusses = ceil(Common Trusses before waste × (1 + Waste Factor ÷ 100))
Gable End Trusses = 2 (non-mono roofs, when included) — no waste factor applied
Truss count uses the same on-center spacing formula as field studs, rafters, and floor joists. Gable end trusses are a fixed count (one per gable end), not a spacing-formula piece count.
Step 3 — Truss-to-Wall Connectors
Connectors = Total Common Trusses × 2 (both bearing points)
Each common truss typically bears on the wall at two points, each commonly needing a rated connector (hurricane tie or truss anchor) resisting wind/seismic uplift. Gable end truss fastening (typically toe-nailed/strapped along the wall) isn't included in this count.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Truss type / span | fink / 30 ft | Sets whether run is half or full span |
| Pitch | 5/12 (22.62°) | Sets rise, height, and chord length |
| Spacing / length | 24" O.C. / 36 ft | Sets the truss count |
Step 1 — Truss Geometry
| Calculation | Result |
|---|---|
| Run | 180" |
| Rise | 75" |
| Top chord length | 195" |
| Overhang tail | 13" |
| Overall height (bearing to ridge) | 75" |
Step 2 & 3 — Truss Count, Gable Ends & Connectors
| Calculation | Result |
|---|---|
| Common trusses before waste | 19 |
| Total common trusses (with 10% waste) | 21 |
| Gable end trusses | 2 |
| Truss-to-wall connectors | 42 |
Therefore, this 30 ft span, 5/12 pitch roof needs approximately 23 trusses total (21 common + 2 gable end) and 42 connectors.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.