Engineered Framing Tools
Roof Truss Calculator
Simplify your roof planning with our truss estimator. Calculate the total number of trusses required for a project, determine the total roof surface area for shingles, and find the individual chord lengths for engineered truss quotes.
Roof Truss Calculator
King-Post · Queen-Post · Fink · Howe · Pratt — member lengths & lumber estimate
Fink (W-truss) — cross-section
Roof Geometry
Truss Layout & Lumber
Tip
Choosing the right truss type
King-post suits spans up to 8 m / 26 ft. Queen-post works up to ~11 m / 36 ft. The Fink (W-truss) is the most common residential choice for spans up to 15 m / 50 ft. Howe and Pratt trusses are used in heavier commercial and industrial applications.
Results
Enter values above to calculate
Truss Anatomy & Spacing
Engineered trusses use a series of triangles to transfer the roof load to the exterior walls without needing interior support.
Common Wood Truss Types
| Design | Max Clear Span | Common Use |
|---|---|---|
| King Post | Up to 24 ft | Garages, sheds, small small additions |
| Fink (W-Truss) | Up to 50 ft | Standard residential homes |
| Howe (M-Truss) | Up to 60 ft | Large residential, commercial |
| Scissor | Up to 40 ft | Vaulted / Cathedral ceilings |
Step-by-Step Formulas
1. Individual Truss Geometry
A standard King Post or Fink truss forms a large triangle. The calculator finds the length of the top chords and the bottom chord (span) to determine material per truss.
2. Total Truss Count
Divide the total building length by the on-center spacing (typically 24" or 600 mm). Adding 1 ensures a truss is placed at both the starting and ending walls.
3. Roof Surface Area
This calculates the total square footage of the roof deck supported by the trusses. This is the primary value used for ordering sheathing and shingles.
4. Dead Load Estimation
The truss must support the weight of the roofing material (shingles, slate, or metal) plus snow and wind loads. Understanding the area helps engineers verify truss capacity.
Worked Example
Garage Project: 24 ft span, 36 ft building length, 6/12 pitch, 24" (2 ft) spacing.
Truss Geometry and Lumber
Trusses turn a roof into a set of triangles, and the member lengths follow directly from span and pitch:
- Triangulation Spans Further: Because a truss resolves load into tension and compression along its members, it clears far greater spans than a rafter of the same depth — which is why they carry roofs over open-plan interiors.
- Web Pattern Suits the Span: King-post works for short spans, queen-post and Fink for medium, and Howe or Pratt for longer ones. The pattern determines how many web members you cut and their lengths.
- Site-Built Trusses Need Engineering: Manufactured trusses come with an engineer's stamp and tested plate connections. A truss assembled on site from gussets is not equivalent and will not pass inspection without a design.
Benefits of Using This Calculator
Example Calculations
Three scenarios worked through step by step:
Example 1 — King-Post Truss
Span 16 ft, 6/12 pitch.
Run = 16 ÷ 2 = 8 ft
Rise = 8 × (6 ÷ 12) = 4 ft (ridge height)
Top chord = √(8² + 4²) = 8.944 ft per side
Bottom chord = 16 ft; king post = 4 ft
Total member length = (8.944 × 2) + 16 + 4 = 37.9 ft
Example 2 — Fink (W) Truss
Span 24 ft, 5/12 pitch.
Run = 12 ft; rise = 12 × (5 ÷ 12) = 5 ft
Top chord = √(12² + 5²) = 13.0 ft per side
Bottom chord = 24 ft
Four web members form the W between chords
Ridge height = 5 ft above the bottom chord
Example 3 — Board Feet for a Set
10 Fink trusses, members from 2×6 stock, 90 ft total length each, 10% waste.
Length per truss = 90 ft; 10 trusses = 900 ft
Board feet = (2 × 6 × 900) ÷ 12 = 900 BF
With 10% waste = 900 × 1.10 = 990 BF
Result: order 990 board feet of 2×6
Planning Tip
Planning Tip
Order manufactured trusses early — six to eight weeks of lead time is normal and they are made to your exact span, pitch, and heel height. Treat the numbers here as a take-off and feasibility check; the fabricator will supply the stamped design drawings your inspector will actually ask to see.
Frequently Asked Questions
- What is the standard truss spacing?
- 24 inches on-center (o.c.) is the residential standard. 16" o.c. is used for higher load requirements.
- How many trusses do I need?
- Divide building length by spacing, round up, and add 1. For a 40' building at 2' spacing: (40/2)+1 = 21 trusses.
- Can trusses span any distance?
- Engineered wood trusses can commonly span up to 60-80 feet without interior supports, making them ideal for open-plan homes.
- What is the difference between a truss and a rafter?
- A rafter is a single sloped member relying on a ridge and ceiling joists for support. A truss is a prefabricated triangulated assembly of chords and webs that carries its own load and spans wall to wall without interior bearing.
- Which truss type should I use?
- King-post suits spans up to about 16 ft, queen-post and Fink handle the 16–35 ft range that covers most houses, and Howe or Pratt configurations serve longer industrial spans. Span and loading determine the choice, not appearance.
- Can I build my own roof trusses?
- Only with an engineered design. Manufactured trusses use pressed steel connector plates whose capacity has been tested, and most jurisdictions require a stamped drawing. Site-built gusseted trusses generally will not pass inspection without engineering.
- How far apart are roof trusses spaced?
- Twenty-four inches on centre is the standard for residential work, which suits typical sheathing span ratings. Sixteen-inch spacing appears under heavy snow loads or where a thinner deck is used. The designer sets it with the load case.
- What is truss heel height?
- The vertical depth at the point where the truss meets the wall plate. A raised or energy heel gives room for full-depth insulation over the exterior wall, which prevents the thin cold spot and ice damming that a standard heel creates.
- Do trusses allow attic storage?
- Standard Fink trusses fill the attic with webs and leave no usable space. Attic trusses are a specific type with a clear rectangular room framed inside them, and they cost more and weigh more because the chords carry a floor load.
- How much do roof trusses cost?
- Typically less installed than stick framing an equivalent roof, because fabrication is offsite and erection is fast. Material cost per truss rises with span, pitch, and heel height; the labour saving is where trusses usually win.