Roof Truss Calculator

Types of Roof Trusses

A roof truss is a triangulated framework of wood (or steel) members connected by metal gusset plates that bridges the full width of a building in one piece. The geometry of the webs — not the lumber size — is what sets each truss family's span ceiling. The six families below cover almost every residential and light-commercial roof. Span ranges are typical, varies by manufacturer; the inline diagrams show the web layout you will see on a shop drawing.

Simple Truss Calculator: King Post Span, Cost & Use Case

If you are sizing a shed, porch, or small garage, set the truss type above to King Post and the dashboard works as a simple truss calculator. A King Post is the simplest truss geometry — two top chords, one bottom chord, and a single vertical king post — and it tops out at 16–26 ft of span at 24" o.c. regardless of lumber size, because the geometry (not the member thickness) governs capacity. Expect $80–$150 per truss and a Low complexity rating, making it the cheapest option for short-span outbuildings. Past 26 ft the king post becomes structurally inefficient — switch to a Queen Post or Fink, both of which open the central bay to distribute load across more webs. For habitable structures, even at short spans, order factory-engineered King Post trusses rather than site-building them.

Scissor Truss Calculator: Vaulted Ceilings

A scissor truss calculator checks whether a vaulted ceiling is feasible at your span. Scissor trusses have bottom chords that angle upward and cross near the center, so the interior ceiling pitches with the roof — typically at about half the roof pitch (a 6/12 roof yields a 3/12 interior vault). Practical spans are 20–40 ft, and you lose about 15–20% of span capacity versus a flat Fink under the same snow load because the angled bottom chords reduce structural depth at the center. Cost runs $250–$550 per truss installed. For spans above 40 ft with a vaulted requirement, a parallel-chord or hybrid scissor/Fink layout is the alternative — confirm with the manufacturer and verify against local snow load.

Attic Truss Calculator: Room-in-Attic Sizing

An attic truss calculator takes your building span, desired room width (typically 12–16 ft interior), and roof pitch to size a room-in-attic truss. Practical spans are 24–40 ft, and the truss needs a steeper pitch (8/12 minimum, 10/12 or 12/12 better) to gain ceiling height inside the rectangular central opening. Plan for a 7'6" minimum headroom at center and a 12 ft wide room on a 40 ft span at 8/12 pitch. Cost runs $400–$900 per piece — about 2–3× a Fink — but the premium buys livable square footage, not just truss structure. If the room is essential but span exceeds ~40 ft, an attic truss may not be feasible; in that case a stick-framed rafter roof with a conventional floor system is the alternative.

Mono Truss Calculator: Single Slope Roof Truss

A mono truss calculator sizes a single-slope roof truss — a half-truss with one top chord sloping from a low eave wall up to a higher bearing wall, used on lean-to additions, shed roofs, and modern mono-pitch designs. Practical spans run 16–32 ft, and the single-slope geometry means there is no ridge peak, so the truss depth grows linearly from the low to the high end. A mono truss at 4/12 on a 24 ft span needs roughly 8 ft of depth at the high wall versus about 4 ft on a 24/12 King Post. Cost runs $90–$200 per piece. To use the estimator above as a mono truss calculator, select King Post (the closest geometry for short single-slope spans) and halve the building width, since a mono truss bridges one slope of what a gable truss would span. For the full lean-to rafter framing (including birdsmouth and overhang cuts), use the dedicated shed roof rafter calculator linked below.

Gable Roof Calculator: Truss Count & Span

A gable roof calculator takes the building width and length plus the roof pitch, and returns the truss type, count, and rough package cost for a standard gable-end roof. For a 28 ft × 40 ft home at 6/12 pitch and 24" o.c., the calculator selects a Fink truss (the default for 28–40 ft spans), returns 21 trusses, and estimates roughly $4,200–$10,500 for the package. The estimator on this page doubles as a gable roof calculator: enter the building width as the span, the length as the building dimension for count, and the pitch for reference. For hip roofs, which need a mix of hip, jack, and common trusses, the geometry is more complex — use the dedicated hip and valley rafter guide linked below for hip roof framing, since a hip roof cannot be planned with a single truss type the way a gable can.

Interactive Truss Span Estimator

The dashboard at the top of this page is a live truss roof calculator. Enter your building span, truss spacing, snow load region, and the truss type you are considering. The estimator returns a rough truss count = (span × 12 ÷ spacing) + 1, a span feasibility flag against the selected truss's typical range, and an auto-suggested truss type when your selection cannot cover the span. The selection score matrix below shows how every truss family scores under your current inputs — green Recommended badge on the best fit, red High Risk tag on any type that exceeds its span.

Roof Truss Span Calculator: How the Span Check Works

Used as a roof truss span calculator, the dashboard compares your building span against the typical span range of each truss family — King Post 16–26 ft, Queen Post 26–40 ft, Fink 28–60 ft, Warren 30–60 ft, Scissor 20–40 ft, Attic 24–40 ft — and flags any selection that falls outside its range under the selected load region. The span check is geometry-driven, not member-driven: doubling the lumber size on a King Post will not push it past ~26 ft, because the single king post geometry is what caps the span. The auto-suggest feature picks the smallest truss family that can cover your span at the current load, so you do not overbuy capacity (and cost) you do not need. Treat the span flag as a planning screen, not an engineering value — the manufacturer's stamped drawings are the final word.

Selection Score Matrix

Headers show weights/units. Span fit is weighted 62%, cost 38%. Scores (0–100%) are computed live from your dashboard inputs. Recommended = best overall match; High Risk = type's typical span is below your building span under the selected load.

Performance / Cost Match Rate

Per-type match rate under your current dashboard inputs (span 32 ft, 24" o.c., Moderate load, selected truss Fink).

How to Choose the Right Truss for Your Roof

Constraint-first selection works backwards from your hard limits — span, load, budget, attic need, and site access — to the truss family that survives every constraint at once. Define the constraints first, then map to a truss; do not fall in love with a truss geometry and then try to make the building fit it.

Roof Truss Design Calculator: Constraint-First Selection

Used as a roof truss design calculator, the dashboard above combines span feasibility, load region, cost index, and headroom goal to shortlist the truss families that survive your constraints. Design a truss by working backwards from hard limits: span sets the geometry family (King Post, Fink, Scissor, Attic), load sets the lumber species and plate size, pitch sets the attic headroom, and budget sets the spacing (24" o.c. residential vs. 48" o.c. agricultural). The ordered list below is the design sequence — work through it top-to-bottom and the surviving truss family is your design output. The design calculator does not replace a stamped truss drawing, but it narrows the design space before you call the truss manufacturer.

1. Span constraint: Measure the clear building width the truss must bridge. Under span ≤ 26 ft prefer King Post; under 26–40 ft prefer Fink (Queen Post if a flat ceiling and simple geometry matter); under span > 40 ft Fink/configured trusses become the only practical wood option.
2. Load constraint: Identify your local ground snow load. Under heavy snow (≥ 50 psf), a Fink outperforms a Queen Post by roughly 20% on effective span capacity because the W-web shares load across more members; a Scissor loses ~15–20% of its span versus a flat Fink under the same load.
3. Budget constraint: Under a tight budget with flat ceilings, Fink at 24" o.c. is the baseline. Scissor costs ~25% more than Fink; Attic costs ~2–3× Fink but adds livable square footage that a second story would otherwise require.
4. Attic / headroom constraint: Under vaulted ceiling required choose Scissor; under habitable room required choose Attic. Under neither constraint, never pay for either — a Fink or Queen Post is cheaper.
5. Crane / site access constraint: A truss package needs a crane with a boom long enough to reach the far wall plus truss height. Under no crane access (tight urban lot, steep narrow driveway), site-built rafters may be the only option even though they cost more per square foot.

Under constraint [span ≤ 26 ft, flat ceiling, low snow] prefer King Post, but under constraint [span 28–40 ft, residential, moderate snow] the Fink outperforms King Post by roughly 130% on span capacity at only ~20% higher per-truss cost. Under constraint [span > 40 ft], Fink/configured trusses become the only practical wood option versus King Post — a King Post simply cannot span past ~26 ft regardless of lumber size, because the geometry (single king post) governs the span, not the member thickness.

Span threshold note: when span exceeds ~40 ft, Fink/configured trusses become the only practical wood option. King Post and Queen Post top out at 26 ft and 40 ft respectively; above 60 ft, engineered parallel-chord or steel trusses take over. The estimator above flags this automatically — if your selected truss cannot cover the span, it returns a High Risk tag and auto-suggests the smallest truss family that can.

Truss vs Rafter: Which Is Better?

Trusses and rafters solve the same problem — span the building and hold up the roof — but they get there with completely different load paths. This section goes estimator-deep on the trade-offs so you can decide by scenario instead of by rule of thumb. The homepage has a shorter rafter-vs-truss overview; this page is the selection-grade comparison. You can also run the actual numbers through the main rafter calculator or convert your roof angle with the roof pitch calculator if you need pitch in degrees.

Truss Cost & Price Estimator

This page doubles as a truss price calculator and roof truss cost estimator: the dashboard above returns a rough truss count for your span, and the table below converts that count into a budget range by truss family. Truss pricing varies ±15% with the lumber market, plate size, pitch, and engineering stamp — treat these ranges as planning numbers, not quotes.

Per-Truss Cost by Type and Span

Installed per-truss cost ranges. Lower end = short span / low load; upper end = long span / heavy snow.

Installed Package Cost: Beyond the Per-Truss Price

A complete truss budget adds three line items beyond the per-truss cost. Use the truss estimator count from the dashboard, then add:

• Delivery: $3–$8 per mile from the truss plant, or a flat $200–$600 for regional deliveries within ~75 miles. Long loads (60+ ft trusses) often require an escort vehicle at $300–$700.
• Crane lift: $800–$2,500 per day, depending on boom height. A 40 ft span with a 12/12 pitch truss is roughly 20 ft tall at the apex and needs a crane tall enough to lift it over the wall plate and swing it into place.
• Installation labor: $50–$120 per truss set by a framing crew — typically 1–2 days for a residential package of 20–30 trusses at 24" o.c.

A truss estimator can also compare truss families side by side — try each type with your span and load in the dashboard above to see which survives the constraints at the lowest cost per square foot. For habitable structures, the manufacturer's stamped quote is the only number that matters at order time; the ranges above are a sanity check on that quote.

When you are ready to move from a rough "cost of trusses calculator" answer to an itemized budget — lumber package, plates, delivery, crane, and labor broken out line by line — use our dedicated roof truss cost calculator, which expands this page's per-truss ranges into a full installed-cost worksheet by span and truss type.

Build Your Own Trusses Calculator: DIY Feasibility & Risk

A "build your own trusses calculator" usually means one of two things: sizing a simple truss you plan to fabricate on-site, or estimating materials for a stick-framed rafter roof. The two have very different answers — read the section that matches your goal before you start cutting lumber.

DIY Truss Fabrication: When It's Possible

Site-building wood trusses is feasible only for small outbuildings — sheds, lean-tos, and small garages under ~26 ft span — where a King Post geometry is acceptable and the building is non-habitable. Even then, the gusset plates are the weak link: factory trusses use 20-gauge galvanized steel plates pressed under 5,000+ PSI hydraulic pressure, which cannot be replicated with screws or nails. Plywood gussets (1/2" or 5/8" CDX) with structural screws (e.g., 1/4" head structural screws) can substitute for light loads, but only on a published, dimensioned plan — never on a layout you sketched yourself.

Why DIY Trusses Are Risky for Habitable Structures

For any structure that supports living space — a home, garage with living above, or accessory dwelling — site-built trusses are illegal in nearly all IRC jurisdictions without an engineer's stamped design. The risk is catastrophic, not incremental: truss geometry transfers load through webs and plates as a system, and a single under-sized gusset or misplaced screw can transfer load to members never designed for it. Insurance carriers routinely deny claims on DIY truss failures, and most building departments will red-tag the structure on inspection. The savings of $80–$150 per King Post truss are not worth the structural, legal, and insurance exposure on a habitable building.

The Safer DIY Alternative: Stick-Framed Rafters

If you want to frame your own roof and don't want to order engineered trusses, the safer path is stick-framed rafters. The IRC prescriptive span tables let a carpenter size 2x rafters for spans up to ~20–25 ft at 24" o.c. without an engineer, and the carpentry is well within reach of an experienced DIYer with a framing square and string line. Use the main rafter calculator to size rafters, rafter count, and pitch — it is built for site-framed carpentry, not truss engineering. If you need usable attic space under the roof, rafters leave that volume open by default; an attic or room-in-attic truss, by contrast, frames the room inside the truss envelope for a 2–3× per-truss premium.

Truss Height & Angle Calculator: Rise, Pitch & Chord Geometry

Beyond span and truss count, two numbers define what a truss actually looks like: how tall it is at the peak and what angle the top chords are cut at. Both follow directly from the roof pitch, so you can calculate truss height and truss angles with nothing more than the building span and the X/12 pitch you plan to frame at. This section is a pure geometry truss calc — the member sizing and engineering checks stay with the manufacturer.

Truss Height Calculator: Peak Rise Above the Bottom Chord

A truss height calculator uses the same rise-over-run math as any gable roof. Half the truss span is the run, and the peak height above the bottom chord is the run multiplied by the pitch ratio:

peak height (in) = (span ÷ 2) × (pitch ÷ 12)

Worked examples for common residential spans and pitches:

Note this is the rise above the bottom chord. Overall truss height adds the heel height — the vertical distance at the bearing point between the bottom of the sitting flat bottom chord and the top edge of the top chord, typically 4–12 in depending on lumber depth and overhang style. If you instead need the height of the roof above the wall plate (for siding, zoning, or window layout), use the dedicated roof height calculator, which converts pitch and half-span into ridge height.

Truss Angle Calculator: Calculating the Top-Chord Cuts

Calculating truss angles is a one-step arctangent: the top chord makes an angle with horizontal of atan(pitch ÷ 12). Every cut on the truss keys off that single number — the plumb cut at the peak, the matching plumb cut at the heel, and the seat cut where the top chord bears on the bottom chord:

The peak itself is a double plumb cut: both top chords are cut at the same angle so they meet flush at the ridge line, and the cut line stays vertical (plumb) when the truss stands in place. For the full cut-angle vocabulary — plumb cut vs. seat cut vs. side cuts, plus degree readouts for any X/12 pitch — see the rafter angle calculator, which covers the identical geometry from the stick-framing side.

Shed Roof Truss Design Calculator: The 12 ft Shed Example

A shed roof truss design calculator answers three questions for a small gable shed: what truss family fits the span, how tall the truss is, and how many you need. Sheds sit squarely in King Post territory (this page's 16–26 ft family, and the cheapest at $80–$150 per truss). Here is the full worked example for the classic 12 foot shed roof truss design at 4/12 pitch:

• Span: 12 ft building width → King Post family (shortest, cheapest truss type).
• Peak height: (12 ÷ 2) × (4 ÷ 12) = 24 in above the bottom chord.
• Top-chord angle: atan(4 ÷ 12) = 18.43° — the same angle on both plumb and seat cuts.
• Top-chord length (no overhang): √(6² + 2²) = 6.32 ft ≈ 6 ft 3-7/8 in per side.
• Truss count: a 10 ft long shed at 24" o.c. = (10 × 12 ÷ 24) + 1 = 6 trusses; at 16" o.c. = 9 trusses.
• Budget: 6 King Post trusses at $80–$150 ≈ $480–$900 before delivery.

Member sizing (chord depth, gusset plate layout, fastener schedule) must come from a published plan or an engineer — geometry is what a calculator can give you, engineering is what keeps the roof up. And if by "shed roof" you mean a single-slope lean-to attached to a taller wall (rather than a free-standing gable shed), that is a mono-truss or stick-rafted roof; use the lean-to roof calculator for the single-slope rafter layout, birdsmouth, and overhang.

Truss Measurements: Part Names and Key Dimensions

Truss measurements use a vocabulary that mixes roof-framing and factory terms. When you call a truss plant, these are the dimensions they will ask for — and the ones a truss length calculator computes behind the scenes:

• Span: the overall width the truss bridges, outside to outside of wall bearings — the bottom chord length (heel to heel).
• Overall height: bottom of bottom chord to the peak; equals peak rise plus heel depth.
• Heel height: vertical depth of the truss at the bearing point (typically 4–12 in).
• Top chord length: heel to peak along the slope = √(run² + rise²); add the overhang length for the ordering length.
• Overhang / cantilever: top-chord extension past the bearing point — 12–24 in on typical eaves; the horizontal return is often called the sub-fascia point or "lookout" side.
• Spacing: the on-center distance truss to truss (24" o.c. residential, 48" o.c. agricultural) — drives the truss count, not the member sizes.

A truss length calculator is just Pythagoras applied to the run and rise — the same math as the shed example above — repeated for each web. Webs themselves (king post, queen posts, W-webs, V-webs) are cut to whatever length closes each triangle, which is exactly why trusses are ordered, not computed on site: the plant's layout software solves every member length at once.

Wendricks Truss Calculator: Third-Party Reference Tools Compared

The "Wendricks truss calculator" (often searched as wendrick truss calculator) refers to the estimating tool offered by Wendricks Truss, a truss manufacturer — a vendor calculator intended to generate a quote-style estimate for their own engineered product. We are not affiliated with them; we mention it because it is a useful reference point when comparing tools. In practice the two serve different stages of the same decision:

• Manufacturer tools (Wendricks and similar): quote-oriented. They price actual engineered trusses from that plant's lumber, plate, and labor costs — best used once you know which truss family and span you need.
• This page: selection-oriented. It compares King Post, Queen Post, Fink, Warren, Scissor, and Attic families by span feasibility, headroom, complexity, and planning cost before you ever request a quote.

A sensible workflow is to narrow the truss family here with the span estimator above, then take that shortlist to one or more manufacturer calculators — including the Wendricks tool — for real pricing in your delivery region. Collecting two or three manufacturer estimates is standard practice, since truss pricing varies ±15% with the lumber market and each plant runs its own engineering software.