Roof Truss Calculator
Plan the trusses for a gable roof. Enter the span, building length, pitch, overhang and spacing, and pick a King post, Queen post, Fink or Howe truss. Get the number of trusses, height, chord and web lengths, cut angles, a lumber buy list and a material cost — with a span check, a live truss drawing, comparison tables and a downloadable PDF.
| Member | Size | Qty | Length each | Buy |
|---|---|---|---|---|
| Enter the span and pitch to list the members | ||||
| Truss | Typical span | Webs | Lumber / truss | Joints | Cost / truss |
|---|---|---|---|---|---|
| Enter the span and pitch to compare | |||||
| Pitch | Angle | Height | Top chord | Lumber / truss | Total cost |
|---|---|---|---|---|---|
| Enter the span and pitch to compare | |||||
How to use the roof truss calculator
Four quick steps turn your span, pitch and spacing into the truss count, height, chord and web lengths, cut angles, a lumber buy list and a material cost — with a span check, a live truss elevation, by-type and by-pitch tables, a chart and a downloadable report.
Enter the building
Give the truss span, building length and the on-center spacing to count the trusses.
Set the roof shape
Enter the roof pitch, eave overhang and any raised heel for attic insulation.
Pick a truss type
Choose King post, Queen post, Fink or Howe, and the top and bottom chord lumber.
Read results & save a PDF
Get the cut list, board feet, cost per truss and total, then download a report.
How a roof truss is laid out
A truss is right-triangle geometry on the top chord plus a web pattern inside. The calculator sizes every member on its centerline, then buys it from stock lumber lengths. Here is the exact math it runs.
Worked example — 24 ft span, 40 ft long, 24″ o.c., 6/12 pitch, 12″ overhang, Fink, 2×4 chords
Rise: 12 × 6/12 = 6 ft · Top chord: 12 × 1.118 + tail ≈ 14'6" · Bottom chord: 24 ft
Webs: 4 (W pattern) across 7 joints · Lumber: ≈ 84 lf (56 bf) per truss
Cost: $63 lumber + $42 gussets = $105/truss · Count: 40×12÷24 + 1 = 21
≈ 21 Fink trusses at about $105 each — roughly $2,205 in framing lumber and gussets for the roof.
Roof truss reference charts
Handy lookups for how the truss type and roof pitch change the webs, lumber, joints and cost.
| Truss | Typical span | Webs | Lumber / truss | Joints | Cost / truss |
|---|---|---|---|---|---|
| King post | to ~26 ft | 1 | 68 lf | 4 | ~$75 |
| Queen post | to ~32 ft | 4 | 92 lf | 7 | ~$111 |
| Fink (W) | to ~40 ft | 4 | 84 lf | 7 | ~$105 |
| Howe | to ~40 ft | 5 | 92 lf | 8 | ~$117 |
More webs and joints mean more lumber and more gussets. The King post is lightest but only suits short spans; the Fink carries the most span for the least material, which is why it’s the standard house truss.
| Pitch | Roof angle | Truss height | Top chord | Lumber / truss | Total cost |
|---|---|---|---|---|---|
| 4/12 | 18.4° | 4′ 0″ | 13′ 8″ | 80 lf | ~$2,142 |
| 5/12 | 22.6° | 5′ 0″ | 14′ 1″ | 84 lf | ~$2,205 |
| 6/12 | 26.6° | 6′ 0″ | 14′ 6″ | 84 lf | ~$2,205 |
| 7/12 | 30.3° | 7′ 0″ | 15′ 1″ | 90 lf | ~$2,300 |
| 8/12 | 33.7° | 8′ 0″ | 15′ 7″ | 90 lf | ~$2,300 |
| 10/12 | 39.8° | 10′ 0″ | 16′ 11″ | 100 lf | ~$2,457 |
| 12/12 | 45.0° | 12′ 0″ | 18′ 5″ | 110 lf | ~$2,614 |
A steeper pitch raises the peak and lengthens the top chords and webs, so lumber per truss climbs — a 12/12 truss uses about a third more lumber than a 4/12 of the same span.
| Building length | 24″ o.c. | 16″ o.c. |
|---|---|---|
| 24 ft | 13 | 19 |
| 32 ft | 17 | 25 |
| 40 ft | 21 | 31 |
| 60 ft | 31 | 46 |
Count = length × 12 ÷ spacing + 1 (one truss at each end). Tighter 16″ spacing is for heavy snow loads and roughly a third more trusses.
What the roof truss calculator gives you
Span, pitch and truss type give you the full member layout plus a lumber buy list and cost.
Roof trusses at a glance
Who uses a roof truss calculator
From a backyard shed to a house or a pole barn, the same calculator lays out the trusses and the lumber.
Framing a shed or detached garage roof and wants a truss count, cut list and lumber cost.
- Set span and pitch
- Pick King or Fink
- Read the cut list
Planning a house roof and wants chord lengths, a raised heel for insulation and a material budget.
- Add a raised heel
- Choose the chord size
- Budget per truss
Pricing a roof package and needs board feet, joints and total lumber cost across every truss.
- Enter lumber prices
- Check board feet
- Export the PDF
Tips for planning roof trusses
Good truss planning comes from the right type for the span, an engineered design and not forgetting bracing and end trusses.
Roof truss calculator FAQ
Quick answers about truss count, spacing, types, height, lumber and building your own.
Divide the building length by the truss spacing and add one for the end truss. At 24 in on-center, a 40 ft long building needs 40 × 12 ÷ 24 + 1 = 21 trusses.
Drop to 16 in on-center for heavy snow loads and the count rises to about 31.
24 inches on-center is standard for residential roof trusses. 16 inches on-center is used for heavy snow loads, thinner roof sheathing or where the truss design calls for it.
Always follow the engineered truss drawing for your project.
A King post has a single center post and suits short spans like garages and sheds (to about 26 ft). A Queen post has two posts at the third points (to about 32 ft).
A Fink has W-shaped webs and is the most common house truss (to about 40 ft). A Howe uses vertical posts and diagonals for longer or heavier spans.
The rise equals the run (half the span) × pitch ÷ 12, and the top chord equals the run × √(1 + (pitch÷12)²), plus the overhang tail.
A 24 ft span at a 6/12 pitch gives a 6 ft rise and a top chord of about 14 ft 6 in with a 12 in overhang.
A raised (energy) heel adds height where the truss meets the wall so full-depth attic insulation fits over the top plates without being squeezed thin.
A standard heel is near zero; 6 to 12 inches is common for an energy heel, and it adds short heel posts and a little overall height.
It depends on span, pitch and type. A 24 ft Fink truss at a 6/12 pitch in 2×4 lumber works out to about 84 linear feet (roughly 56 board feet) per truss once stock lengths and web waste are counted.
That’s two top chords, one bottom chord and four webs across seven joints.
You can shop-build simple trusses, but US building codes require trusses to be built to an engineer’s truss design drawing with the right lumber grades, connector plates and bracing for your loads.
Use this calculator to estimate lumber and cost, then have the design engineered and approved.
Usually yes for the structure overall. Trusses use smaller lumber and go up fast with less skilled labor, and they clear-span the building so you can skip load-bearing interior walls.
Stick-framed rafters give more usable attic space but cost more in labor and bigger lumber.
Planning & estimating only — not an engineered design. US building codes require trusses to be built to an engineer’s truss design drawing, with lumber grades, connector plates and bracing sized for your snow, wind and dead loads — this tool does not check strength. Rise = run × pitch ÷ 12 and top chord = run × √(1 + (pitch÷12)²); lengths are measured on member centerlines. Lumber prices are placeholders, so enter your local prices, and the spans listed for each truss type are rough rules of thumb, not design limits.