# Truss Calculator

Free truss calculator for roof truss design. Get truss height, rafter length, truss length, member count, roof truss cost, and number of trusses for spans up to 40 feet. Supports king, queen, and fink truss types.

## What this calculates

A truss is the engineered triangular frame that supports a pitched roof. Sizing trusses correctly means getting the span, pitch, spacing, and member geometry right before ordering or building. This free truss calculator works through the whole simple truss calculator workflow: truss height, rafter length, total truss length with overhang, number of trusses, web member count, and an engineered truss cost estimate.

## 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 basic truss geometry is a right triangle:

- **Half span** = building span / 2
- **Truss height** = half span * (pitch / 12)
- **Rafter length** = sqrt(half span^2 + height^2)
- **Truss length with overhang** = rafter length + overhang

This truss length calculator formula handles symmetric gable trusses with the peak at centerline. Asymmetric trusses and scissor trusses need different math (consult engineered drawings).

## Roof Truss Design Calculator Basics

A roof truss design calculator picks truss type based on span:

| Span | Recommended Type | Webbing |
|------|------------------|---------|
| Under 20 ft | King post | 1 vertical member |
| 20-30 ft | Queen post | 2 verticals + horizontal |
| Up to 40 ft | Fink (W-truss) | 4 diagonal/vertical members |
| 40-60 ft | Howe or parallel chord | Engineered only |
| Over 60 ft | Commercial engineered | Sealed drawing |

For most residential homes, the fink (W-truss) covers spans up to 40 ft with 2x4 chords and webbing.

## Truss Length Calculator Example

For a 24 ft span, 6:12 pitch, and 12 in overhang:

- Half span = 12 ft
- Truss height = 12 * 6 / 12 = 6 ft
- Rafter length = sqrt(12^2 + 6^2) = sqrt(180) = 13.42 ft
- Truss length with overhang = 13.42 + 1 = **14.42 ft per top chord**

This truss length calculator output is what you order from a truss plant per side.

## Roof Truss Span Calculator

A roof truss span calculator validates whether your span is safe for standard 2x4 trusses:

- Span under 20 ft: 2x4 top chord at 24 in OC, 30 PSF live load
- Span 20-30 ft: 2x4 or 2x6 top chord at 24 in OC
- Span 30-40 ft: 2x6 required; engineer sealed drawing recommended
- Span over 40 ft: commercial engineered only

Double the spacing from 24 in to 16 in OC if adding snow load over 40 PSF, tile roofing, or solar panels.

## Truss Cost Calculator / Roof Truss Cost

A truss cost calculator uses engineered truss pricing per linear foot of span:

- **2025 residential engineered truss (2x4 webbing):** $3-6/ft of span
- **Heavy engineered (2x6):** $6-10/ft of span
- **Pole-barn truss (gable, 20-40 ft):** $6-12/ft of span

Roof truss cost example: a 40 ft x 24 ft ranch with 6:12 pitch and fink trusses at 24 in OC needs 21 trusses at ~$108 each = **$2,268 for engineered trusses**. Installation adds $2-4 per sq ft of roof area.

Roof truss prices home depot on 84 Lumber network: a pre-built 24 ft fink truss with 6:12 pitch runs **$100-140 each**, matching our estimate within 10%.

## Truss Design Calculator vs Truss Analysis Calculator

A truss design calculator outputs geometry (height, length, member count) and cost. A truss analysis calculator solves the member forces under load (tension, compression in each member) using the method of joints or method of sections. This tool is a truss design calculator; use engineered software (MiTek SAPPHIRE, Alpine Software, or free tools like SkyCiv) for truss analysis.

## Simple Truss Calculator Assumptions

A simple truss calculator makes standard assumptions:

- **Symmetric gable truss:** peak at centerline, equal slopes both sides
- **Standard overhang:** 12-24 in horizontal
- **2x4 chords at 24 in OC:** covers spans up to 30 ft at standard residential load
- **No point loads:** uniform dead + live load
- **Wood frame:** SPF, SYP, or Doug fir; engineered trusses specify species

For scissor trusses, asymmetric designs, cantilevers, or commercial loads, always use an engineered truss design calculator with sealed drawings.

## Truss Analysis Calculator Reference Numbers

Quick reference for truss member forces under uniform load (approximate):

- **Top chord (rafter):** compression, 2,000-5,000 lb at 40 PSF live load, 40 ft span
- **Bottom chord:** tension, equal magnitude to top chord
- **Webs:** alternating tension/compression, 500-1,500 lb each

Always cross-check with stamped engineering drawings before building.

## Frequently Asked Questions

**Q: What does a free truss calculator output?**

A: A free truss calculator outputs truss height at the peak, rafter length (the hypotenuse from peak to wall), total truss length including eave overhang, number of trusses for your building length, web member count by truss type, total lumber for site-built trusses, and an estimated cost based on per-foot-of-span truss pricing.

**Q: How does a simple truss calculator differ from a truss analysis calculator?**

A: A simple truss calculator handles geometry and cost (truss height, rafter length, number of trusses, member count). A truss analysis calculator solves member forces (tension and compression in each chord and web) under load using engineering methods. This tool is a simple truss calculator and truss design calculator; truss analysis needs engineering software.

**Q: What is the roof truss cost for a 40 ft span?**

A: Roof truss cost for a 40 ft span in 2025 runs $3-6 per foot of span per truss, so a single 40 ft engineered fink truss is $120-240. A 40 ft by 60 ft building at 24 in OC needs 31 trusses, totaling $3,720-7,440 before installation. Roof truss prices home depot and 84 Lumber match within 10% for standard 2x4 webbing.

**Q: What does a roof truss span calculator check?**

A: A roof truss span calculator checks whether the span is safe for standard 2x4 trusses. Spans up to 20 ft use 2x4 at 24 in OC. 20-30 ft usually uses 2x4 but may need 2x6. 30-40 ft requires 2x6 top chords. Over 40 ft needs engineered commercial trusses with sealed drawings.

**Q: What is the truss length calculator formula?**

A: Truss length calculator formula: truss length = sqrt((span/2)^2 + height^2) + overhang. Height = (span/2) x (pitch/12). Example: 24 ft span, 6:12 pitch, 12 in overhang = sqrt(12^2 + 6^2) + 1 = 14.42 ft per top chord.

**Q: Can I use a truss cost calculator to compare suppliers?**

A: Yes. A truss cost calculator with $3-6 per foot of span pricing covers most residential quotes. Call 3 truss plants (84 Lumber, Builders FirstSource, local mills) with your span, pitch, spacing, and building length. Compare quoted prices to the calculator output. Variances of 10-20% reflect regional differences; over 30% usually means a spec mismatch.

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Source: https://vastcalc.com/calculators/construction/truss
Category: Construction
Last updated: 2026-04-08