Roof Truss Calculator — Quick Planning Estimate
This free tool helps you plan roof framing in minutes. Enter your building span (width), length, roof pitch, truss spacing, and overhang. The calculator returns a recommended truss count, key geometry (rafter length and ridge height), roof area, and a materials takeoff for chords, webs, sheathing, and roofing. It’s ideal for early budgeting and material ordering. For structural design and stamped drawings, always work with a licensed engineer or a truss manufacturer.
How to Use This Roof Truss Calculator
- Enter the span (clear width, plate to plate) and length along the ridge.
- Select your on-center spacing (16 in, 19.2 in, 24 in — or metric equivalents).
- Choose a roof pitch (e.g., 4/12, 6/12) and set the overhang.
- Click Calculate to see truss count, rafter length, ridge height, and materials.
- Adjust the waste allowance (5–15%) to fit your job and cutting pattern.
Understanding Pitch, Span & Area
Pitch is expressed as rise over run. In Imperial mode, 6/12 means the roof rises 6 inches for every 12 inches of horizontal run. In Metric mode, the same pitch is displayed as 500 mm rise per 1 m run. We use the slope factor √(1 + (rise/run)²) to convert plan area to sloped roof area and estimate top-chord lengths.
Raised-Heel Trusses (Energy-Friendly)
Raised-heel trusses lift the top chord at the eaves to make room for full-depth insulation over the exterior wall. Toggle Raised heel to add extra heel height in your geometry and materials. This detail improves energy performance and helps meet modern energy codes.
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FAQs
How many roof trusses do I need?
Enter the building length and your on-center spacing (16 in, 19.2 in, or 24 in). The calculator estimates truss count as ceil(length ÷ spacing) + 1 to include both end trusses, and rounds up.
Will this calculator engineer my trusses?
No. This is a planning tool for estimating quantities and basic geometry. Final truss design and bracing must be provided by a licensed engineer or truss manufacturer per local codes.
What does 6/12 roof pitch mean?
A 6/12 pitch rises 6 inches for every 12 inches of horizontal run (about 26.6°). In metric mode, the same pitch is shown as 500 mm rise per 1 m run.
How many sheathing sheets will I need?
We estimate sloped roof area from plan area and pitch, apply your waste allowance (default 10%), then divide by 32 ft² per 4×8 sheet and round up.
What spacing should I use—24 in or 16 in?
24 in o.c. is common for engineered trusses in many regions; 16 in o.c. can reduce deflection but increases truss count and cost. Follow local codes and truss supplier guidance.
Accuracy & Review
Reviewed by: Caleb Wright
Caleb validates our roofing calculators, reviewing shingle coverage assumptions, waste factor guidance, and ventilation recommendations. He focuses on practical jobsite accuracy to help ensure estimates reflect real-world installation conditions.
Last updated:
See: Methodology · Data Sources · Review Board
Important Estimate Disclaimer
Results are preliminary estimates only and do not replace professional roofing specifications. Material quantities may vary based on pitch complexity, waste factors, underlayment layers, and local code requirements.
Review our Methodology and Data Sources for calculation details.
Wind exposure, flashing requirements, and structural considerations may affect final material totals.