Roof Truss Calculator: Count, Height & Chord Length
6min Read
Posted 6.30.2026
🦉 Roof Truss Calculator
Get your truss count, peak height, and top chord length from four inputs.
Assumes a common gable (Fink-style) truss with a 12″ overhang on each eave. Peak height is measured from the top of the wall plate. Always have final truss engineering done by the manufacturer — Minnesota snow loads require stamped designs.
Talk Through Your Project — Free →How the Roof Truss Calculator Works
Trusses are the engineered triangles that hold your roof up, and estimating them takes exactly four numbers: the span (building width the truss must bridge), the building length, the roof pitch, and the spacing between trusses. The calculator divides length by spacing and adds one for the end (a 48-ft building at 24″ on center needs 25 trusses, not 24 — the classic fence-post error), then uses right-triangle geometry to find peak height and top chord length from your span and pitch.
It covers the standard gable truss that frames most garages, sheds, pole barns, and simple homes. Hip ends, girder trusses, attic trusses, and scissor trusses are specialty designs the manufacturer engineers separately.
Roof Truss Spacing: 24″ vs. 16″ On Center
Residential trusses are typically set 24 inches on center — the spacing virtually all manufactured trusses are engineered for under normal loads. You will see 16″ spacing on some older construction, heavy tile or slate roofs, or where long sheathing spans need extra support. Tighter spacing means more trusses and cost but a stiffer roof plane. If you are matching an existing structure, measure center-to-center on the current trusses before ordering anything.
How to Calculate Truss Height (Why It Matters for Permits)
Peak height = half the span × pitch ÷ 12. A 30-ft-wide garage at 6/12 pitch peaks 7’6″ above the wall plates. This number matters more than people expect: municipal height limits for accessory buildings, sight lines, and even HOA rules are all driven by it. Bump that same garage to 10/12 and the peak jumps to 12’6″ — enough to blow past many suburban detached-garage height caps. Run the pitch options above before you fall in love with a steep roofline. Our roof pitch calculator converts any pitch to degrees if your city measures that way.
Top Chord Length and Sheathing Math
The top chord is the sloped member your roof deck attaches to. Its length = (half-span + overhang) × the pitch multiplier, and it drives your sheathing and shingle count: total roof area is building length × total chord run × 2 planes. The calculator reports that area so you can jump straight to our roofing calculator for squares, bundles, and underlayment on the same project.
Truss Costs and Minnesota Snow Loads
Stock gable trusses for a garage run roughly $4–$6 per foot of span at lumberyards — a 30-ft truss lands around $120–$180, so our 25-truss example is $3,000–$4,500 in trusses before delivery and crane time. The critical Minnesota wrinkle: snow load. Most of the metro requires trusses engineered for a 35 psf ground snow load, and stamped engineering sheets are required for permits. Never re-use or modify trusses without an engineer’s sign-off — cutting a single web member can compromise the entire triangle, and we have seen the sagging rooflines that prove it.
Trusses vs. Rafters: Which Should You Use?
Trusses are factory-built, cheaper per foot, faster to set, and engineered for exact loads — the default for new garages and additions. Stick-framed rafters make sense when you want vaulted or usable attic space, are matching historic framing, or the site will not allow truss delivery. Rafters demand more carpentry skill and usually cost more in labor. Many remodels end up hybrid: trusses over the garage, rafters over the great room.
Roof Truss FAQs
How many trusses do I need for a 24×24 garage?
At 24″ on center: 13 trusses (24 ÷ 2 + 1). At 16″ spacing: 19.
How far apart are roof trusses?
Standard residential spacing is 24 inches on center; 16 inches for heavier loads or specific engineering.
How tall is a 6/12 truss on a 30-foot span?
7 feet 6 inches from the wall plate to the peak, before any overhang or heel height.
Can I buy trusses without engineering?
Suppliers provide stamped engineering with every order — required for Minnesota permits due to snow loads. Keep the sheets for your inspection.
Do trusses include the overhang?
Yes — you specify overhang (typically 12–24 inches) when ordering, and it is built into the top chord.
Planning a garage, addition, or full re-frame? Owl Roofing can walk the structure, coordinate the roofing side, and give you straight answers — reach out for a free consult. 🦉
