How many roof trusses do I need?

Divide your building length by the on-center spacing, round up, then add 1 for the end truss. For a 40 ft building at 24 inch spacing: ceil(40 / 2) + 1 = 21 trusses. At 16 inch spacing: ceil(40 / 1.333) + 1 = 31 trusses. Enter your dimensions in the calculator above for an instant count.

What spacing should I use for roof trusses — 24 in or 16 in?

24 inch on-center spacing is standard for most engineered roof trusses. 16 inch spacing reduces deflection and bounce but increases truss count and cost. Some roofing products or heavier dead loads may require tighter spacing. Always follow your truss manufacturer's specifications and local building code.

What does 6/12 roof pitch mean?

A 6/12 pitch rises 6 inches for every 12 inches of horizontal run — approximately 26.6 degrees. In metric, this is 500 mm rise per 1,000 mm (1 m) run. The pitch determines rafter length (top chord), ridge height, and total sloped roof area. Steeper pitches increase material quantities significantly.

Will this calculator engineer my trusses?

No. This is a planning tool for estimating quantities and basic geometry only. Final truss design, member sizing, connector plates, and bracing must be provided by a licensed engineer or truss manufacturer with stamped drawings per local codes. Never use this calculator as a substitute for engineered drawings.

How many sheathing sheets do I need for a roof?

Calculate sloped roof area (plan area x pitch factor), add your waste allowance, then divide by 32 sq ft per 4x8 sheet and round up. For a 40x24 ft building at 6/12 pitch: plan area = 960 sq ft x slope factor 1.118 = 1,073 sq ft + 10% waste = 1,181 sq ft / 32 = 37 sheets. The calculator above handles this automatically.

What is a raised heel truss?

A raised heel truss (also called an energy heel) lifts the top chord at the eave to allow full-depth insulation over the exterior wall plate. This improves thermal performance and helps meet modern energy codes. The heel height typically adds 6-12 inches above the standard heel. Toggle the raised heel option in the calculator to include this in your geometry estimate.

Roof Truss Calculator – How Many Trusses Do I Need?

Planning estimates only, final truss design must be by a licensed engineer or truss manufacturer per local codes.

Units

Building width / span (ft)

Building length (ft)

Truss spacing (in)

Common engineered truss spacings.

Roof pitch (rise per 12 in run)

Rise (in)

Run (in)

Example: 6/12 ≈ 26.6° (≈ 500 mm rise per 1 m run).

Eave overhang (in)

Waste / overage (%)

Truss type

Heel type

Roof Truss Calculator — Truss Count, Spacing & Materials Guide

This calculator estimates truss count, rafter length, ridge height, roof area, sheathing sheets, and a lumber materials takeoff. Enter your building span, length, pitch, and on-center spacing. It supports imperial and metric units, three truss types, and raised heel geometry.

Truss Count by Building Length & Spacing

Building length	16" o.c.	19.2" o.c.	24" o.c.
20 ft	16 trusses	13 trusses	11 trusses
30 ft	23 trusses	19 trusses	16 trusses
40 ft	31 trusses	26 trusses	21 trusses
50 ft	39 trusses	32 trusses	26 trusses
60 ft	46 trusses	38 trusses	31 trusses

Includes both end trusses. 40 ft building highlighted as common residential reference. Add gable end trusses and special trusses (hips, valleys, girders) separately.

Pitch Factor Reference

Pitch	Angle	Slope factor	Rafter per ft of half-span	Area increase
4/12	18.4°	1.054	1.054 ft	+5.4%
5/12	22.6°	1.083	1.083 ft	+8.3%
6/12	26.6°	1.118	1.118 ft	+11.8%
8/12	33.7°	1.202	1.202 ft	+20.2%
10/12	39.8°	1.302	1.302 ft	+30.2%
12/12	45.0°	1.414	1.414 ft	+41.4%

6/12 highlighted as most common residential pitch.

How Truss Count Is Calculated

The formula: truss count = ceil(building length ÷ spacing in feet) + 1. The +1 accounts for the end truss. For a 40 ft building at 24" spacing: ceil(40 ÷ 2) + 1 = 21 trusses.

This is a planning estimate for standard gable trusses. Hip roofs, valleys, dormers, girder trusses, and gable end trusses add to the count and require manufacturer input. Final engineering must come from a licensed truss plant with stamped drawings.

Frequently Asked Questions

Divide building length by spacing in feet, round up, add 1 for the end truss. For a 40 ft building at 24" spacing: ceil(40 ÷ 2) + 1 = 21 trusses. At 16" spacing: ceil(40 ÷ 1.333) + 1 = 31 trusses. See the quick reference table above for common combinations, or enter your dimensions in the calculator.

24 inch on-center is standard for most engineered roof trusses and is the most economical. 16 inch reduces deflection and bounce but increases truss count and cost significantly. Some heavy roofing materials, snow loads, or specific products may require tighter spacing. Always follow your truss manufacturer's specifications and local building code.

A 6/12 pitch rises 6 inches for every 12 inches of horizontal run — approximately 26.6 degrees. In metric: 500 mm rise per 1,000 mm run. This is one of the most common residential pitches in North America. Steeper pitches (8/12, 10/12) significantly increase rafter length and roof area — see the pitch factor table above.

No. This is a planning tool for quantities and basic geometry only. Final truss design including member sizing, connector plates, camber, bracing, and uplift values must be provided by a licensed engineer or truss manufacturer with stamped drawings per local codes. Never use this calculator as a substitute for engineered drawings.

Calculate sloped roof area (plan area × pitch slope factor), add your waste allowance, then divide by 32 sq ft per 4×8 sheet and round up. For a 40×24 ft building at 6/12 pitch: 960 sq ft × 1.118 = 1,073 sq ft + 10% waste = 1,181 sq ft ÷ 32 = 37 sheets. The calculator handles this automatically.

A raised heel (energy heel) truss lifts the top chord at the eave to allow full-depth insulation over the exterior wall plate. Standard trusses compress insulation at the eaves, reducing thermal performance. The raised heel height is typically 6–12 inches and helps meet modern energy codes. Toggle the raised heel option in the calculator to include this in your geometry.

Roof Truss Planning Checklist

Reviewed by Caleb Wright. Covers span measurements, pitch verification, spacing layout, bearing conditions, bracing, sheathing sequencing, and safety before ordering trusses.

Download Checklist (PDF)

Planning reference only. See Methodology and Data Sources. View all project checklists →

Accuracy & Review

Reviewed by: Caleb Wright

Caleb validates our roofing calculators, reviewing shingle coverage assumptions, waste factor guidance, pitch factor formulas, and practical measurement conventions to ensure estimates reflect real-world installation conditions.

Last updated: Feb 12, 2026

See: Methodology · Data Sources · Review Board

Related Roofing Calculators

Roof Square Footage Calculator Roof Pitch Calculator Shingle Calculator Plywood Calculator Lumber Calculator Concrete Footing Calculator

Disclaimer: Results are preliminary estimates only and do not replace professional roofing or structural specifications. Final truss design, bracing, and stamped drawings must be provided by a licensed engineer or truss manufacturer.

See Methodology and Data Sources for details.