Introduction
Trusses are engineered, but the takeoff isn’t always obvious. Chord lengths, web member totals, and gusset plate counts all depend on the truss profile. Get them wrong and you’re either short on lumber or you’ve overpaid. This roof truss calculator handles the geometry in one pass. Pick a truss type, enter building span, length, and pitch. The tool returns truss count at your chosen spacing, actual spacing after rounding, top chord length (with and without overhang), bottom chord length, approximate web member length, lumber per truss, and total lumber. It also reports gusset plate size, plates per truss, total plates, and total plywood area. Add unit costs and you get a total installed estimate plus cost per truss. Contractors use it for framing bids. Owner-builders use it to sanity-check a truss package before ordering.
How to Use the Roof Truss Calculator
Choose your currency and unit system. Sixteen currencies and both imperial and metric are supported.
Enter building span and length. Span is wall-to-wall. Length runs along the ridge.
Set the roof pitch. Rise:12, degrees, or percent all work.
Add the overhang, bearing width, and heel height. Bearing width is usually the wall plate thickness. Heel height raises the top chord for full-depth insulation.
Pick a truss type. Fink, Howe, Queen Post, King Post, Scissor, Attic, Raised Heel, Mono, Hip, or Custom.
Set truss spacing. 24 inches is standard. 16 inches for heavy snow loads.
Pick a lumber size. 2×4 through 2×10 presets.
Choose gusset plate size and sides. 12-inch plywood is standard, one each side of the joint.
Add a ridge board if your design needs one, then enter unit costs and read the result.
How the Roof Truss Calculator Formula Works
Truss geometry starts with clear span. Clear span is building span minus two bearing widths. That’s the distance the truss actually has to bridge.
Formula: Truss Span = Building Span − (2 × Bearing Width)
Formula: Run (per side) = Truss Span ÷ 2
Formula: Rise = Run × Pitch Ratio
Formula: Peak Height = Rise + Heel Height
Formula: Top Chord (each) = Run ÷ cos(atan(Pitch Ratio)) + Overhang ÷ cos(atan(Pitch Ratio))
Formula: Bottom Chord = Truss Span
Formula: Truss Count = Ceiling(Building Length ÷ Spacing) + 1
Formula: Gusset Plates = Plates per Joint × Sides × Truss Count
Bottom chord length equals clear span, since it runs straight between the two wall plates. Top chord length is the hypotenuse of rise and run, plus the overhang extension. Pitch ratio is rise over 12 converted to a decimal.
Web members use a multiplier tied to truss type. A King Post has the fewest webs at 0.85 times the top chord run. An Attic truss has the most at 1.9 times, since it has to carry floor loads and creates usable attic space. The calculator applies the right multiplier automatically.
Truss count depends on building length and spacing. A 40-foot building at 24 inches on center gives 21 trusses. Actual spacing after rounding usually lands slightly less than 24 inches, which the tool reports separately.
Gusset plates are counted per joint. The truss type sets the joint count (Fink has 8, Howe has 10, King Post has 4). Multiply that by the number of sides per joint, then by the total truss count.
Worked Example
A 34-foot span, 44-foot building length, 5:12 pitch, 18-inch overhangs, 3.5-inch bearing at each end. Fink/W truss, 2×6 lumber, 24-inch spacing. 12-inch gusset plates, two sides per joint.
Step 1 — Clear span. 34 − 2 × 0.292 = 33.42 ft.
Step 2 — Run per side. 33.42 ÷ 2 = 16.71 ft.
Step 3 — Pitch ratio. 5/12 = 0.4167. Angle = 22.62°.
Step 4 — Rise. 16.71 × 0.4167 = 6.96 ft.
Step 5 — Peak height (no raised heel). 6.96 ft.
Step 6 — Top chord without overhang. 16.71 ÷ cos(22.62°) = 16.71 ÷ 0.9233 = 18.10 ft.
Step 7 — Overhang along slope. 1.5 ft ÷ 0.9233 = 1.62 ft.
Step 8 — Top chord with overhang (each side). 18.10 + 1.62 = 19.72 ft.
Step 9 — Total top chord per truss. 19.72 × 2 = 39.44 ft.
Step 10 — Bottom chord. 33.42 ft.
Step 11 — Web members (Fink, factor 1.35). 1.35 × 18.10 = 24.44 ft.
Step 12 — Lumber per truss. 39.44 + 33.42 + 24.44 = 97.30 ft.
Step 13 — Truss count. Ceiling(44 ÷ 2) + 1 = 23 trusses. Actual spacing = 44 ÷ 22 = 2.00 ft, or 24.00 inches.
Step 14 — Total lumber. 97.30 × 23 = 2,237.9 ft.
Step 15 — Gusset plates. 8 joints × 2 sides × 23 trusses = 368 plates.
Step 16 — Gusset plywood. 368 × 1 ft² = 368 ft² (12-in plates).
Step 17 — Cost at $0.85/ft lumber, $3.50 per gusset, $4.50/ft ridge board (44 ft), $45 per truss labor, $200 hardware.** Lumber = $1,902.22. Gussets = $1,288. Ridge = $198. Labor = $1,035. Material subtotal = $3,388.22 + hardware = $3,588.22. Total = $4,623.22. Cost per truss = $201.01.
Interpretation: Order 23 Fink trusses at 24 inches on center. You need about 2,238 feet of 2×6 lumber, 368 gusset plates, and roughly 368 square feet of 12-inch plywood. Material and labor together run about $4,600, or roughly $200 per truss.
