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 uses ceil(length/spacing)+1 to include end trusses and rounds up.

Will this calculator engineer my trusses?

No. This is a planning tool for estimating quantities and geometry. Final truss design must be performed by a licensed engineer or truss manufacturer per local codes.

What does 6/12 roof pitch mean?

6/12 pitch rises 6 inches for every 12 inches of horizontal run (about 26.6°). The slope factor is sqrt(1+(6/12)^2), which the tool uses for roof area and chord length.

How many sheathing sheets will I need?

We multiply the sloped roof area by a waste allowance (default 10%) and divide by 32 ft² per 4×8 sheet, then 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. reduces deflection and increases truss count and cost. Follow local codes and supplier guidance.

Roof Truss Calculator | Home Project Calculators

Planning estimates only—final truss design must be by an engineer or truss plant per local codes.

Units

Building Width / Span (ft)

Building Length (ft)

Truss Spacing (in)

Roof Pitch (rise per 12 in)

Rise

Run

Example: 6/12 ≈ 26.6°

Eave Overhang (in)

Waste / Overage (%)

Truss Type

Heel Type

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).
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 12 in of run. A 6/12 roof rises 6 in vertically for every 12 in horizontally and has a slope factor of √(1+(6/12)²) ≈ 1.118. We use that slope factor to convert plan area to sloped area and to compute chord lengths. The span is the clear distance between bearing walls. Half of that span, combined with the pitch, gives you the rafter length and ridge height.

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.

Related Roof Tools

Keep planning with these calculators:

Limitations & When to Call a Pro

This calculator gives planning quantities only. It does not size members, design connections, or account for snow/wind uplift. Hip roofs and specialty trusses (scissor, attic/room-in-truss) require shop drawings from a truss manufacturer. When in doubt, consult a licensed professional.