TryBuildCalcRoof Truss Calculator (Truss Count, Geometry & Connectors)
Find your roof truss count and height 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
26
24 common (+10% waste) + 2 gable end
Overall Truss Height
7.00 ft
84" from bearing to ridge peak
Truss Geometry
Type: fink
Pitch: 6/12 (26.57° from horizontal)
Run: 168" (14.00 ft)
Rise: 84" (7.00 ft)
Top chord length: 187.83"
Overhang tail: 13.42" (12" horizontal overhang)
Overall height (bearing to ridge): 84"
Truss Count
Spacing: 24" O.C. over 40 ft
Common trusses before waste: 21
Total with 10% waste: 24
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: 48
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: 24 pcs + recommended tools
+−
Bill of Materials
Main material: 24 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.
What Is a Roof Truss Calculator?
A roof truss calculator finds the number of prefabricated roof trusses, their basic geometry (height, chord length, overhang), gable end truss count, and truss-to-wall connector hardware needed for a roof — the dominant residential roof-framing method in the US for anything beyond a simple small roof. It starts from your building span (the full clear span a truss covers) and length (the direction trusses are spaced along), applies the same on-center spacing formula used for wall studs and floor joists, and computes truss height and chord length from direct trigonometry.
This calculator does not design trusses. Every prefabricated wood truss is an engineered component — a truss designer sizes its members, web layout, and metal connector plates using manufacturer-specific software, then produces a stamped, sealed design drawing for fabrication. This tool estimates count and geometry for planning and takeoff only.
Why truss type and heel selection matter here:
- A scissor truss's vaulted ceiling rise depends on BOTH the top and bottom chord pitch — enter both separately
- A raised/energy heel adds real height at the bearing point, changing the truss's overall height and often required by modern energy codes
- A mono (single-slope) truss uses the full building span as its run, with no ridge and no gable end trusses
- Gable end trusses are typically a different product (vertical-stud or step-down) than common trusses, not counted by the same spacing formula
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 / 28 ft | Sets whether run is half or full span |
| Pitch | 6/12 (26.57°) | Sets rise, height, and chord length |
| Spacing / length | 24" O.C. / 40 ft | Sets the truss count |
Step 1 — Truss Geometry
| Calculation | Result |
|---|---|
| Run | 168" |
| Rise | 84" |
| Top chord length | 187.83" |
| Overhang tail | 13.42" |
| Overall height (bearing to ridge) | 84" |
Step 2 & 3 — Truss Count, Gable Ends & Connectors
| Calculation | Result |
|---|---|
| Common trusses before waste | 21 |
| Total common trusses (with 10% waste) | 24 |
| Gable end trusses | 2 |
| Truss-to-wall connectors | 48 |
Therefore, this 28 ft span, 6/12 pitch roof needs approximately 26 trusses total (24 common + 2 gable end) and 48 connectors.
Essential Checklist+−
Complete these critical checks before approving the work or proceeding to the next construction stage.
✓Truss Design Inputs+-
- Building span and length confirmed from actual field measurements or plans, not assumed
- Roof pitch entered matches the actual design intent, not a rough guess
- Truss spacing matches the roof sheathing/decking span rating and the actual roof load for this project
- Local building code edition, wind/seismic zone, and snow load confirmed before finalizing
✓Truss Engineering & Design+-
- Confirmed this calculator does NOT replace an engineered, stamped truss design — a real truss order/design was obtained separately
- Truss placement diagram from the manufacturer matches the actual roof plan and this takeoff's count
- Girder trusses (trusses that carry other trusses, e.g. at a valley or opening) identified and engineered separately
- Damaged or incorrectly-cut trusses are never modified in the field without engineering approval
✓Bracing & Installation+-
- Temporary erection bracing planned and installed as each truss is set — before it's left unsupported
- Permanent bracing (web member bracing, continuous lateral bracing) installed exactly per the truss designer's drawing
- Truss-to-wall connectors (hurricane ties/truss anchors) rated for the site's actual wind/seismic uplift requirement
✓Installation & Code Compliance+-
- Permit and framing inspection requirements confirmed before roof sheathing covers the trusses and their bracing
- Wide spans, unusual loads, or any non-standard condition reviewed by the truss designer or a structural engineer
Full QC Checklist+−
Verification checklist for prefabricated wood roof truss material takeoffs — covering span/pitch inputs, truss engineering and design, bracing and installation safety, and code compliance. Use the Essential Checklist for critical checks before finalizing, expand to Full QC Checklist for complete verification.
✓Truss Design Inputs+-
- Building span and length confirmed from actual field measurements or plans, not assumed
- Roof pitch entered matches the actual design intent, not a rough guess
- Truss type selected matches the actual roof design (common, scissor, attic, mono, etc.)
- Truss spacing matches the roof sheathing/decking span rating and the actual roof load for this project
- Calculation confirmed to represent one clear-span truss run at a time
- Local building code edition, wind/seismic zone, and snow load confirmed before finalizing
✓Truss Engineering & Design+-
- Confirmed this calculator does NOT replace an engineered, stamped truss design — a real truss order/design was obtained separately
- Truss placement diagram from the manufacturer matches the actual roof plan and this takeoff's count
- Girder trusses (trusses that carry other trusses, e.g. at a valley or opening) identified and engineered separately
- Damaged or incorrectly-cut trusses are never modified in the field without engineering approval
- Gable end truss type (vertical-stud vs. step-down ladder) confirmed against the actual gable overhang detail
✓Bracing & Installation+-
- Temporary erection bracing planned and installed as each truss is set — before it's left unsupported
- Permanent bracing (web member bracing, continuous lateral bracing) installed exactly per the truss designer's drawing
- Truss-to-wall connectors (hurricane ties/truss anchors) rated for the site's actual wind/seismic uplift requirement
- Gable end truss fastening and any required L-bracing/stiffener bracing installed per the truss drawing
- Crane lift plan (if used) confirmed against actual truss weight, span, and site access — not assumed
✓Installation & Code Compliance+-
- Roof sheathing, underlayment, and roofing material planned and estimated separately
- Attic/roof ventilation (soffit, ridge, or gable vents) planned to match the actual truss heel and ridge detail
- Permit and framing inspection requirements confirmed before roof sheathing covers the trusses and their bracing
- Wide spans, unusual loads, or any non-standard condition reviewed by the truss designer or a structural engineer
Framing Reference Tables
Common roof pitches and their angle/diagonal-length factor, and the truss types this calculator models.
| Pitch | Angle from Horizontal | Diagonal Length Factor (per ft of run) |
|---|---|---|
| 3/12 | 14.0° | 1.031 |
| 4/12 | 18.4° | 1.054 |
| 6/12 | 26.6° | 1.118 |
| 8/12 | 33.7° | 1.202 |
| 9/12 | 36.9° | 1.250 |
| 12/12 | 45.0° | 1.414 |
Truss Types
| Type | Description |
|---|---|
| Fink / Common (W-truss) | Classic W-shaped web pattern — the most common residential truss for a given span/load, economical and widely available. |
| King Post | Single vertical web at the center — simplest layout, typically used for shorter spans. |
| Queen Post | Two vertical webs — a step up from king post for slightly longer spans. |
| Howe | Web members that form a series of triangles from the ridge — often used for longer spans. |
| Fan | Web members fan out from the bottom chord — an alternative long-span layout. |
| Scissor (Vaulted Ceiling) | Top and bottom chords at two different pitches, opening a vaulted/cathedral ceiling inside. |
| Attic (Room-in-Attic) | Bottom chord raised to create usable attic floor space (room-in-attic) below the roof line. |
| Mono (Single-Slope) | Single continuous slope, full building span as the run — used for additions, porches, and lean-tos. |
Truss type here is informational/geometric only — every truss's actual member sizes and web layout are engineered by the truss designer, regardless of the type selected in this calculator.
When should you use this roof truss calculator?
- Planning truss count and rough geometry for a new roof, room addition, garage, or shed before ordering.
- Estimating gable end trusses and truss-to-wall connector hardware alongside the common truss count.
- Finding overall truss height for site planning, ceiling height coordination, or crane clearance.
- Comparing how pitch, heel type, or spacing changes total truss count and height before finalizing a design.
- Cross-checking a supplier's truss quote against an independent estimate before ordering.
Quick Framing Tips
- Get the actual engineered truss design and placement diagram from your supplier before ordering — this calculator is a planning estimate, not the final order quantity.
- Never modify a truss in the field (cutting, notching, or altering a chord/web) without the truss designer's approval — it can compromise its engineered capacity.
- Install temporary bracing immediately as each truss is set — an unbraced truss (or partial group) is a leading cause of collapse during construction.
- Follow the permanent bracing layout on each truss's own engineered drawing — bracing needs vary by truss design, not a one-size-fits-all spacing.
- Confirm a raised/energy heel gives enough clearance for a ventilation baffle above the insulation at the eave.
- A 10% waste factor is a reasonable estimating default — increase it for a roof with many intersecting sections or a complex plan.
Common Mistakes
- Treating this calculator's output as the final order quantity instead of confirming against the manufacturer's engineered placement diagram.
- Leaving trusses unbraced (even temporarily) between setting and permanent bracing/sheathing — a well-documented cause of job-site collapse.
- Field-cutting or notching a truss chord or web member without engineering approval to make it fit.
- Forgetting that girder trusses (carrying other trusses at a valley or opening) need separate, heavier engineering than a standard common truss.
- Using undersized or unrated truss-to-wall connectors instead of confirming the actual uplift requirement for the site's wind/seismic zone.
- Confusing a scissor truss's bottom chord pitch with its top chord pitch — they're two different, independently-set values.
- Not leaving enough raised heel height for a ventilation baffle above full-depth insulation at the eave.
Limitations
- US light-frame residential prefabricated wood truss practice only — steel trusses, non-US framing conventions, and site-built (stick-framed) roof structures are not modeled (see this site's Rafter Calculator for stick-framed common rafters).
- Does not design trusses — member sizes, web layout, and metal connector plates must come from a truss designer using manufacturer-specific software and a stamped, sealed design drawing, not this calculator.
- Does not compute permanent or temporary bracing layout, sizes, or spacing — follow the truss designer's own drawings and the industry-standard BCSI (SBCA/TPI) guide.
- Does not identify or size girder trusses, hip/valley sets, or jack trusses — these need specific engineering from the truss manufacturer, outside this calculator's scope.
- Does not count fasteners (beyond the truss-to-wall connector count), roof sheathing, underlayment, or roofing material.
- Assumes a single, simple gable (or mono) roof plane with uniform span, pitch, and spacing — does not handle hip roofs, multiple intersecting roof sections, or dormers in one calculation.
- Truss-to-wall connector count assumes 2 bearing points per common truss and does not verify the connector's actual uplift rating against your site's wind/seismic zone.
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.