The roof truss handbook.
Straight talk on the decisions that actually move your material count, your cost, and your permit approval. Written for framers, contractors, and owner-builders. No fluff, no upselling.
📐 BASED ON
IRC 2021 · SBCA · AWC NDS
ASCE 7-22 · TPI-1
01 · OVERVIEW
What is a truss calculator?
A truss calculator is a purpose-built tool for figuring out the geometry, lumber requirements, and material costs of roof trusses before you order or build them. Enter your building's span, roof pitch, and length. You get back the number of trusses needed, rafter length, peak height, and a ballpark cost estimate.
Roof trusses are pre-engineered structural frames that carry the weight of your roof to the exterior walls. Getting the numbers wrong means either over-ordering (wasted money) or coming up short mid-project. Builders use truss calculations at the design stage to check feasibility, prepare material lists, and get quotes from truss manufacturers.
This tool handles the six most common residential truss types: King Post, Queen Post, Fink/W, Howe, Scissor, Attic, and Gambrel. It accounts for eave overhang in its rafter length calculations. The underlying formulas follow the International Residential Code (IRC) geometry standards. See our methodology for details on how each output is derived.
02 · TRUSS TYPES
King Post vs Fink trusses.
King Post trusses are the simplest design: two rafters meeting at a peak with a single vertical post dropping to the center of the bottom chord. They're solid for spans up to about 20 feet, which makes them ideal for sheds, small garages, and covered porches. Above 20 feet, a King Post starts to flex in the middle under snow and live loads unless you add a horizontal tie.
Fink trusses (also called W-trusses) add a web of diagonal and vertical members that distribute loads more efficiently. They handle spans from 20 to 40+ feet with less lumber than any other common truss type. The SBCA reports Fink trusses account for roughly 70% of all residential truss production in North America. For a standard home, Fink is almost always the right starting point. Deep dive on all six truss types →
03 · ROOF PITCH
Choosing the right roof pitch.
Roof pitch affects every downstream cost: lumber length, sheathing area, shingle count, and labor time. Low-slope roofs (3/12 to 4/12) are cheaper to frame but require heavier-duty waterproofing and can accumulate debris. Mid-range pitches (5/12 to 7/12) are the most common in residential construction across the continental U.S. They drain well, look proportional, and don't add dramatically to framing cost.
In heavy snow regions, steeper pitches help shed loads passively. Above 8/12, you'll need staging and safety equipment during installation, which adds labor cost. According to IRC Section R802, the minimum slope for asphalt shingles is 2/12; for most tile roofing, 4/12 is the code minimum. Full roof pitch guide →
04 · SPACING
Truss spacing for different applications.
The standard residential truss spacing is 24 inches on center. This works with 7/16-inch OSB or 1/2-inch plywood sheathing and spans most code-required live loads (20 psf in most U.S. zones). Tightening to 16 inches makes sense if you're in a high snow load area (60+ psf ground snow load), if your roof covering is heavy (concrete tile exceeds 9 lbs/sq ft), or if you're using thinner sheathing.
Moving to 48-inch spacing (common in commercial and agricultural buildings) requires engineered trusses with heavier chords and more webbing. The truss unit cost goes up, but you need fewer of them. Run both spacing options through the calculator above to compare totals. Full spacing comparison →
05 · COST
Estimating lumber and material costs.
Pre-built trusses from a manufacturer typically cost $3.50–$6.00 per linear foot of span, depending on complexity. A 30-foot Fink truss fabricated and delivered runs roughly $175–$200 per unit in most markets. That puts a 21-truss order for a 40-foot building at $3,675–$4,200 for the trusses alone, not counting installation labor, which typically adds $1.50–$3.00 per linear foot of span per truss for crane placement.
Lumber prices fluctuate, so the estimates in this calculator are based on 2024–2026 industry surveys by the SBCA and should be treated as planning figures. 2026 truss cost breakdown →
WHO THIS IS FOR
Should you use this calculator?
General contractors & builders
Use it at the estimating stage to ballpark truss counts and costs before ordering engineering drawings. Not a substitute for stamped shop drawings, but solid for a bid.
DIY homebuilders & owner-builders
Planning garages, additions, or new homes? Check whether your dimensions are realistic before paying for architectural drawings.
Structural estimators
Verify proposed roof geometry against height restrictions or HOA limits before submitting permit drawings.
Permit applicants
Generate the span, pitch, and peak height numbers most building departments want to see on applications.
For complex roofs or engineered timber framing, consult a licensed structural engineer. The Structural Building Components Association (SBCA) maintains a directory of certified truss designers if you need professional sign-off.