Roof Truss Calculator

Calculate how many roof trusses you need, member lengths, and total cost for your building

Calculate how many trusses your building needs

Quick presets

ft

Trusses/Rafters Needed

1

24" spacing • 0.0 ft rafter length

PRO

Professional Calculator

Load calculations, truss spacing, and code compliance

ft
ft

Estimated Materials

53 bundles

Roof Area

1,581 sq ft

Squares

15.8

Detailed Breakdown

Roof Area1,581 sq ft
With Waste1,739 sq ft
Roofing Squares15.8
Bundles53
How to Use This Calculator
The Roof Truss Calculator has three tabs to help you plan your truss order from start to finish.

Truss Count tab: Enter your building length in feet and select the on-center spacing (24" is standard residential, 16" for heavy loads or long spans). The calculator divides the building length by the spacing and adds one, then adds gable end trusses. It accounts for both common and gable-end trusses so you get the exact quantity to order.

Truss Dimensions tab: Enter your building span (width) and roof pitch to see the computed rafter (top chord) length, bottom chord length, truss height at peak, and overhang tail length. These dimensions help you verify your truss shop drawings and ensure trusses will fit on the delivery truck. The calculator supports Fink, Howe, Pratt, scissor, and attic truss types.

Cost Estimate tab: Enter your truss count and span to get an estimated per-truss price and total cost. Prices are based on 2026 US averages and vary by span, truss type, and region. The calculator optionally adds delivery cost, which typically runs $500-$1,500 per load. For the most accurate pricing, request quotes from at least two local truss manufacturers.

The Formula
The truss calculator uses these formulas:

Truss Count = (Building Length in inches ÷ Spacing in inches) + 1 + Gable End Trusses For a 40 ft building at 24" OC: (480 ÷ 24) + 1 + 2 = 23 trusses

Rafter (Top Chord) Length = (Span ÷ 2) ÷ cos(pitch angle) + Overhang For a 30 ft span at 5/12 pitch: (15) ÷ cos(22.6°) + 1.5 = 16.25 + 1.5 = 17.75 ft

Truss Peak Height = (Span ÷ 2) × (Pitch Rise ÷ 12) For a 30 ft span at 5/12: 15 × (5/12) = 6.25 ft above the top plate

Cost Estimate = Truss Count × Per-Truss Price + Delivery Standard Fink truss pricing (2026): - 20-24 ft span: $100-$180 per truss - 26-30 ft span: $150-$250 per truss - 32-36 ft span: $250-$350 per truss - 38-40 ft span: $350-$450 per truss
Example Calculation
Example: 40 ft Ranch Home in Ohio

Mark is building a 40 × 30 ft ranch home with a 5/12 pitch gable roof.

Step 1: Truss Count
• Building length: 40 ft = 480 inches
• Spacing: 24" on center
• Common trusses: (480 ÷ 24) + 1 = 21 common trusses
• Gable ends: 2 gable end trusses
• Total: 23 trusses

Step 2: Truss Dimensions
• Span: 30 ft, half-span (run): 15 ft
• Pitch: 5/12 → angle = 22.6°
• Rafter length: 15 ÷ cos(22.6°) = 16.25 ft + 1.5 ft overhang = 17.75 ft top chord
• Bottom chord: 30 ft + (2 × 1.5 ft overhang) = 33 ft
• Peak height: 15 × (5/12) = 6.25 ft above the wall plate

Step 3: Cost Estimate
• 23 Fink trusses at 30 ft span: 23 × $200 = $4,600
• 2 gable end trusses: 2 × $150 = $300
• Delivery: $800
• Crane rental (half day): $500
• Total truss package: ~$6,200
• Installation labor (1 day, 3-person crew): ~$1,800
• Total installed: ~$8,000

Frequently Asked Questions

How many trusses do I need for a 40-foot building?
For a 40-foot building with standard 24-inch on-center spacing: (40 ft x 12 in/ft) / 24 in + 1 = 21 common trusses, plus 2 gable end trusses, for a total of 23 trusses. If you use 16-inch spacing for heavy snow loads, you need (40 x 12) / 16 + 1 = 31 common trusses plus 2 gable ends = 33 total.
How much does a roof truss cost in 2026?
In 2026, a standard Fink truss for a 24-30 ft span costs $100-$250 each. Larger spans (36-40 ft) run $250-$450 each. Specialty trusses like scissor or attic trusses cost 30-60% more. Delivery typically adds $500-$1,500 depending on distance and quantity. Total installed cost including crane and labor is roughly $5-$10 per square foot of roof area.
What is the standard spacing for roof trusses?
The standard spacing for residential roof trusses is 24 inches on center (OC). For areas with heavy snow loads, longer spans over 30 feet, or when using heavier roofing materials like tile, 16-inch OC spacing is recommended. Some structural insulated panel (SIP) systems allow 48-inch spacing.
What is the maximum span for a roof truss?
Standard wood roof trusses can span up to 60 feet, though spans over 40 feet require heavier lumber (2x6 or 2x8 chords) and engineered designs. Most residential trusses span 20-36 feet. For spans exceeding 60 feet, steel trusses or engineered wood products are typically required. Always consult a structural engineer for spans over 40 feet.
Should I use trusses or rafters for my roof?
Trusses are faster to install, more cost-effective for most homes, and engineered for consistent quality. Rafters (stick-framing) offer more attic space and flexibility for complex roof shapes, but cost 20-30% more in labor. Trusses are the preferred choice for about 80% of new residential construction. Use rafters if you want a vaulted ceiling without scissor trusses, or if your roof geometry is too complex for standard truss designs.

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Related Guides & Resources

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