Roof Truss Calculator

Count and price a truss package with this roof truss calculator: truss quantity including gable end frames, bracing lumber, hurricane ties and a cost range by truss type.

By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.

Quick answer: To count a truss package, divide the building length by the truss spacing, add one, and count the two end frames as gable trusses. A 48 ft long building at 24 in on center takes 25 trusses, which is 23 common trusses plus 2 gable end frames.

Your measurements

Gable end: pitch is the rise over a 12 in run; the factor from that pitch turns footprint into roof area.

Building spanftOutside of wall plate to outside of wall plate, measured on the plates after they are set. Trusses are built to the ordered span and will not seat on a wall that came out wide.Building lengthftThe dimension the trusses run along. On an L-shaped building, count each leg separately and add a girder truss where they meet.Truss spacing24 in on center is the residential standard and lets 7/16 in OSB span the top chords. 16 in is used for heavy snow, clay tile and long spans.Top chord pitchThe pitch the fabricator builds to. It does not change the truss count, but it drives the price, the shipping height and whether an attic truss has usable headroom.OverhanginHorizontal cantilever of the top chord past the wall, measured level. Past 24 in the fabricator has to design the cantilever and it shows on the truss drawing.Truss typeA scissor truss typically costs 30 to 40 percent more than a common truss of the same span, and an attic truss three to four times as much.Price per truss (optional)$Enter the quoted price for one common truss to replace the typical range. Gable end frames are quoted separately and usually run 10 to 25 percent more.

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Results

Trusses to order: 25 trusses; 23 common at 24 in on center over 48 ft plus 2 gable end frames; 28 ft span, 31 ft out to out with the overhangs
Truss package cost: $2,800 to $5,000; Common trusses typically run $4.00 to $7.00 per foot of span in 2026, so about $112 to $196 each at this span. Freight is separate
Bracing lumber: 312 ft; 20 sticks of 2x4 at 16 ft: 4 continuous restraint rows the length of the building plus 12 diagonals. An allowance only, since the truss drawings and BCSI set the real layout. Warning: BCSI wants a diagonal bracing set at each end of the run and about every 20 ft along it, not just lateral rows
Hurricane ties: 50 ties; Two per truss, one at each bearing. IRC R802.11 sizes this connection for uplift, and high-wind counties often call for a tie on each face of the heel
Setting the trusses: Boom truck or a crew; At 28 ft of span a crew can set these by hand with enough people, but a boom truck is faster and safer. Brace the first truss to the ground first
Planning estimate: Engineered component; A truss is designed and sealed by the fabricator. IRC R802.10.4 prohibits cutting, notching or drilling any member without written approval from a registered design professional, and the truss drawings must be on site for the inspector

Roof Truss formula

Trusses = Building length (in) / spacing, rounded up, + 1
Gable end frames = 2 (the first and last position);  Commons = Trusses - 2
Bracing rows = (Span / 10, rounded up, - 1) + 1 or 2 web rows
Bracing lumber = Rows x Length + Rows x (Length / 20, rounded up) x 10 ft

Worked example

A 60 ft long building with a 32 ft span, scissor trusses at 16 in on center. 60 x 12 = 720 in / 16 = 45 bays, plus 1, so 46 trusses: 44 scissor commons and 2 gable end frames. At $5.50 to $9.00 per foot of span, each truss is $176 to $288, and the package with the gable premium lands near $8,200 to $13,400 before freight.

Bracing: the 32 ft span takes 3 bottom chord rows and 2 web rows, so 5 rows x 60 ft = 300 ft, plus 5 rows x 3 diagonal sets x 10 ft = 150 ft, for 450 ft of 2x4, which is 29 sticks of 16 ft. Hurricane ties: 46 x 2 = 92. A 32 ft span is past the point where a crew should pike trusses up by hand, so price a crane.

Quick reference

Trusses by building length and spacing, with a typical 28 ft common truss package at 24 in on center
Building length	24 in on center	16 in on center	Package at 24 in on center
24 ft	13	19	$1,500 to $2,600
32 ft	17	25	$1,900 to $3,400
40 ft	21	31	$2,400 to $4,200
48 ft	25	37	$2,800 to $5,000
56 ft	29	43	$3,300 to $5,800
64 ft	33	49	$3,700 to $6,500
80 ft	41	61	$4,600 to $8,100

Counting and pricing a truss package

The count is the building length divided by the spacing, plus one, because trusses sit at both ends of every bay. A 48 ft building at 24 in on center is 24 bays and 25 trusses. Two of those are gable end frames rather than common trusses: they are flat-bottomed frames with vertical studs at 16 or 24 in so the end wall sheathing and siding have something to catch. They are quoted separately and typically run 10 to 25 percent more than a common truss of the same span.

Price scales with span and type. A common Fink truss typically runs $4.00 to $7.00 per foot of span in 2026, a scissor truss $5.50 to $9.00, and an attic truss $12 to $20 because it carries a floor load. A girder truss for a hip end is two or three plies nailed or bolted together and is priced per ply. Freight is a separate line and a long truss is an oversize load, so ask what the delivery charge is before you compare two quotes. Lead time in most markets runs 3 to 8 weeks, and it stretches every spring.

A truss is an engineered component, not a stick of lumber

Every truss is designed by the fabricator to ANSI/TPI 1 and comes with a truss design drawing that lists the span, pitch, loads, plate sizes and any continuous lateral restraint the webs need. IRC R802.10.1 requires those drawings on site and approved before the trusses go up, and the inspector will ask for them. IRC R802.10.4 prohibits cutting, notching or drilling a member without written approval from a registered design professional. That includes the bottom chord a plumber wants to pass a drain through and the web an HVAC crew wants gone.

Bracing is where truss jobs go wrong. Temporary restraint holds the trusses while they are being set; permanent bracing stays in the roof forever. BCSI, the SBCA guide the IRC accepts under R802.10.2, calls for continuous lateral restraint rows along the bottom chords and any marked webs, and a diagonal bracing set at each end of the run and about every 20 ft along it. Lateral rows alone do nothing without diagonals; they just tie the whole run together so it can fall as one piece. Brace the first truss back to the ground or to a braced wall before anything hangs on it.

What this calculator leaves out

The truss design itself, which comes from the fabricator once you give them the span, pitch, overhang, loads and ceiling type. Girder trusses and hip sets, which are priced per ply and often need a hanger schedule. Freight and the crane, typically $700 to $2,000 for a half day in most markets. Sheathing, subfascia, blocking, ceiling drywall backing, energy heels where the code requires full insulation depth over the wall, permit fees, and the engineered hangers a girder needs at each end.

Code limits that apply

IRC R802.10.1checked
Truss design drawings delivered to the job and approved before the trusses are set
If you miss it: No drawings at framing inspection stops the job until the fabricator sends the sealed set
IRC R802.10.2checked
Permanent restraint and bracing per the truss drawings or an approved method such as BCSI
If you miss it: A run braced only for erection racks over in a gust, and every plate then has to be inspected
IRC R802.10.4
No cutting, notching or altering a truss without a design professional's written approval
If you miss it: One cut web downgrades the whole truss; the repair is a sealed detail with plates and scabs on both faces
IRC R802.11
Truss to wall connection designed for uplift, with ties where toenails are not enough
If you miss it: Toenails only in a high-wind county is written up, and the ties go on from a ladder after the roof is sheathed
ANSI/TPI 1
The design standard the IRC references; the fabricator seals each truss design
If you miss it: A truss built to a sketch has no engineering behind it, and no inspector or lender will accept it

Provision	Limit	If you miss it
IRC R802.10.1checked	Truss design drawings delivered to the job and approved before the trusses are set	No drawings at framing inspection stops the job until the fabricator sends the sealed set
IRC R802.10.2checked	Permanent restraint and bracing per the truss drawings or an approved method such as BCSI	A run braced only for erection racks over in a gust, and every plate then has to be inspected
IRC R802.10.4	No cutting, notching or altering a truss without a design professional's written approval	One cut web downgrades the whole truss; the repair is a sealed detail with plates and scabs on both faces
IRC R802.11	Truss to wall connection designed for uplift, with ties where toenails are not enough	Toenails only in a high-wind county is written up, and the ties go on from a ladder after the roof is sheathed
ANSI/TPI 1	The design standard the IRC references; the fabricator seals each truss design	A truss built to a sketch has no engineering behind it, and no inspector or lender will accept it

Rows marked checked produce a warning in the results when an entry crosses the limit. The others are on the plans or on site and this calculator does not test them. Local amendments can be stricter; the adopted edition and the inspector govern.

Mistakes that cost money

Cutting a web to run a duct voids the truss engineering; IRC R802.10.4 requires a design professional's written repair detail before it is covered.
Ordering before the wall plates are set: trusses are built to the ordered span and will not seat on a wall that came out wide.
Leaving gable end frames off the order: a common truss at the end has no vertical studs to nail sheathing and siding to.
Treating BCSI temporary restraint as permanent bracing: the run can fold before the sheathing goes on, and it takes the whole roof.
Storing trusses flat on the ground: the plates rust, the chords take a set, and the fabricator will not warrant them.
Hurricane ties nailed with roofing nails instead of the 8d x 1-1/2 in the report calls for carry a fraction of their rating.

Key facts

IRC R802.10.1 requires the truss design drawings to be provided to the building official and approved before the trusses are installed.
IRC R802.10.4 prohibits cutting, notching or altering any truss member without the written approval of a registered design professional.
Trusses at 24 in on center are the residential standard, so a 48 ft long building takes 25 of them, counting both gable end frames.
A common Fink truss typically costs $4.00 to $7.00 per foot of span in 2026, which is $112 to $196 for a 28 ft span, while an attic truss of the same span runs three to four times that.
ANSI/TPI 1 is the design standard the IRC references for metal plate connected wood trusses, and BCSI from SBCA is the accepted bracing method on site.

Frequently asked questions

How many roof trusses do I need for a 40 ft building?

21 trusses at 24 in on center, which is 19 common trusses and 2 gable end frames. At 16 in on center the same building takes 31. The span does not change the count, only the price of each truss.

How much do roof trusses cost?

A common Fink truss typically runs $4.00 to $7.00 per foot of span in 2026, so $112 to $196 for a 28 ft span. A 48 ft building at 24 in on center needs 25 of them, roughly $2,800 to $5,000 for the package before freight.

Can I cut a roof truss to fit a duct or a window?

No. IRC R802.10.4 prohibits cutting, notching or drilling any truss member without written approval from a registered design professional. A cut web means a sealed repair detail with plates or scabs on both faces, which is slower and more expensive than routing the duct around it.

Are trusses cheaper than stick framing?

Usually, once the span passes about 24 ft. Trusses use smaller lumber, arrive engineered, and a crew can set a roof in a day instead of a week. The trade is that the attic is full of webs, so a truss roof gives you storage rather than living space unless you buy attic trusses.

Sources and references

Chapter 8 Roof-Ceiling Construction, Section R802.10 Wood Trusses, 2021 IRC (ICC)
BCSI, Building Component Safety Information guide to handling, installing and bracing trusses (Structural Building Components Association)
ANSI/TPI 1 standards overview for metal plate connected wood trusses (Truss Plate Institute)
H2.5A hurricane tie for the rafter or truss to top plate connection (Simpson Strong-Tie)

Next steps for this project

The usual order for a roofing & siding project. See all roofing & siding calculators.

Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.