# Truss Calculator Design your roof frame with our free truss calculator. Estimate truss height, rafter length, overall dimensions, and material costs for standard pitched roofs. ## What this calculates A roof truss is the engineered triangular wooden frame that supports a pitched roof. Sizing your trusses correctly requires accurate measurements for your span, pitch, spacing, and member geometry before you start building or placing an order. Our free truss calculator handles the math for you. It quickly determines your truss height, rafter length, total truss length with overhang, required number of trusses, and an estimated total cost. ## Inputs - **Building Span** (ft) — min 6, max 80 — Clear span between supporting walls (outside to outside) - **Roof Pitch** (:12) — min 1, max 24 — Rise per 12 inches of run (4:12 to 12:12 common residential) - **Building Length** (ft) — min 6, max 200 — Length of the building (for truss count) - **Truss Spacing** — options: 12 in O.C., 16 in O.C., 24 in O.C. (standard), 48 in O.C. (with purlins) — 24 in is standard residential; 16 in for heavy loads - **Truss Type** — options: King Post (under 20 ft span), Queen Post (20-30 ft), Fink / W-Truss (up to 40 ft) - **Eave Overhang** (in) — min 0, max 48 — Rafter extension past wall (12-24 in typical) - **Truss Price per Foot of Span** ($) — min 0, max 20 — Engineered 2x4 truss: $3-6 per ft of span (2025). Use 0 to skip cost. ## Outputs - **Truss Height (Peak)** (ft) - **Rafter Length (no overhang)** (ft) - **Total Truss Length (with overhang)** (ft) — Top chord length including overhang - **Number of Trusses** - **Web Members per Truss** — Vertical and diagonal pieces inside the truss - **Total Lumber (site-built)** (linear ft) - **Estimated Truss Cost** — formatted as currency — Engineered trusses: span x price x truss count - **Load Class Guidance** — formatted as text ## Details How the Truss Calculator Works The foundation of basic truss geometry relies on a standard right triangle. Here is how we calculate your dimensions: - Half span: Your total building span divided by two. - Truss height: The half span multiplied by your roof pitch (divided by 12). - Rafter length: The square root of the half span squared plus the height squared. - Total truss length: Your rafter length plus your eave overhang. These formulas apply directly to symmetric gable trusses, where the peak sits perfectly in the center. If you are building asymmetric or scissor trusses, you will need different formulas and should consult engineered drawings. Choosing the Right Truss Design Selecting the correct truss type depends entirely on your building's span: - Under 20 feet (King Post): Uses a single vertical web member. - 20 to 30 feet (Queen Post): Features two vertical members and one horizontal member. - Up to 40 feet (Fink or W-Truss): Uses four alternating diagonal and vertical members. This is the most common choice for residential homes. - 40 to 60 feet (Howe or Parallel Chord): Requires custom engineered designs. - Over 60 feet: Requires commercial engineered designs with sealed structural drawings. Truss Length Calculation Example Let us look at a standard example: a building with a 24-foot span, a 6:12 roof pitch, and a 12-inch overhang. - Half span: 12 feet - Truss height: 6 feet (12 feet multiplied by 6/12) - Rafter length: 13.42 feet - Total truss length: 14.42 feet per top chord (including the 1-foot overhang) When you order from a truss plant, you will use this final 14.42-foot measurement for each side. Validating Your Roof Truss Span Our calculator helps verify if your planned span safely supports standard 2x4 lumber construction: - Under 20 feet: Safely uses 2x4 top chords spaced at 24 inches on center (for a standard 30 PSF live load). - 20 to 30 feet: Usually requires either 2x4 or 2x6 top chords spaced at 24 inches on center. - 30 to 40 feet: Strictly requires 2x6 lumber. We highly recommend obtaining engineer-sealed drawings. - Over 40 feet: Demands commercial engineered trusses. If your roof must support heavy snow loads (over 40 PSF), tile roofing, or solar panels, you should reduce your truss spacing from 24 inches to 16 inches on center to carry the extra weight. Estimating Your Roof Truss Costs Truss manufacturers usually price their products per linear foot of the span. Here are typical 2025 material estimates: - Residential engineered truss (2x4 webbing): $3 to $6 per foot of span - Heavy engineered truss (2x6 lumber): $6 to $10 per foot of span - Pole-barn gable truss (20 to 40 feet): $6 to $12 per foot of span Cost Example: If you build a 40-foot by 24-foot ranch home with a 6:12 pitch and Fink trusses spaced 24 inches on center, you need 21 individual trusses. At roughly $108 each, your materials cost comes to about $2,268. Professional installation generally adds another $2 to $4 per square foot of roof area. Truss Design vs. Truss Analysis It helps to understand the difference between design and analysis tools. A truss design calculator (like this one) outputs the physical geometry, member counts, and estimated costs. A truss analysis calculator does something completely different. It calculates the specific physical forces, like tension and compression, placed on each wooden member under a heavy load. If you need structural analysis, you should use dedicated engineering software. Standard Calculator Assumptions To provide accurate estimates, our simple truss calculator relies on standard residential building assumptions: - Symmetric gable trusses with equal slopes on both sides. - Standard eave overhangs measuring 12 to 24 inches horizontally. - Trusses built with 2x4 chords spaced 24 inches on center (supporting standard residential loads up to 30 feet). - Uniformly distributed dead and live loads across the roof, with no extreme single point loads. - Standard wood framing materials (like SPF, SYP, or Douglas Fir). Basic Truss Force Guidelines If you want a quick reference for how weight impacts a typical 40-foot truss under a standard 40 PSF uniform load: - Top chord (rafters): Handles compression forces of 2,000 to 5,000 pounds. - Bottom chord: Handles tension forces roughly equal to the top chord. - Webbing: Alternate between tension and compression, carrying 500 to 1,500 pounds each. Always cross-check your final plans with stamped, approved engineering drawings before you begin construction. ## Frequently Asked Questions **Q: What information does the truss calculator provide?** A: Based on your building span and roof pitch, we provide the truss height, the length of the rafters, the total length including overhangs, and an estimated cost. **Q: How do I choose the right truss type?** A: For building spans up to 40 feet, the Fink (or W-truss) is the standard and most cost-effective choice for residential construction. **Q: What is a safe roof truss span?** A: Standard 2x4 trusses can safely span up to 30 feet. Spans between 30 and 40 feet require thicker 2x6 lumber and should be verified by a structural engineer. --- Source: https://vastcalc.com/calculators/construction/truss Category: Construction Last updated: 2026-04-21