Roof Truss Calculator
Enter the span, pitch, overhang and heel height. You get the truss height, the top and bottom chord lengths and the web member lengths for four common shapes, with a diagram that updates as you type.
Layout dimensions only. Trusses must be engineered for your loads, span and local code. Truss manufacturers supply stamped drawings.
Truss height at the peak
7 ft 4 in at the peak
Fink (W) · 28 ft span · 6/12 · 26.6°
A Fink truss with a 28 ft span at 6/12 is 7 ft 4 in high at the peak. Each top chord is 16 ft 9¼ in long with the overhang; the bottom chord is 28 ft.
- Rise, heel to peak7 ft
- Heel height4 in
- Top chord, heel to peak (each side)15 ft 7⅞ in
- Overhang tail along the slope1 ft 1⅜ in
- Top chord with overhang (each side)16 ft 9¼ in
- Bottom chord28 ft
- Pitch angle26.57°
- A · Short diagonal (×2)4 ft 5⅞ in
- B · Long diagonal (×2)8 ft 8¼ in
- Web C—
Layout dimensions only, measured node to node on the outer lines of the truss. Trusses must be engineered for your loads, span and local code; the truss maker supplies stamped drawings.
Planning estimate, not a quote. Disclaimer
How the truss dimensions are calculated
A gable truss is a triangle with a flat bottom. The bottom chord is the span. The top chords rise from the bearing points to the peak at your roof pitch, so the rise is half the span times the pitch over 12. A heel height adds a vertical step at each bearing point, which lifts the whole top line. The overhang continues each top chord past the bearing, and it is measured along the slope.
Height at the peak = heel height + rise
Top chord, heel to peak = (span ÷ 2) × √(12² + pitch²) ÷ 12
Overhang tail = overhang × √(12² + pitch²) ÷ 12
Bottom chord = span
All lengths are measured node to node on the outer lines of the truss: the underside of the bottom chord and the top edge of the top chord. A truss maker works from member centerlines and lumber depth, so real cut lengths differ a little. Use these figures for layout, for ordering plans and for checking a drawing.
Example: a 28 ft span at 6/12 with a 4 inch heel and a 12 inch overhang has a rise of 7 ft 0 in and stands 7 ft 4 in high at the peak. Each top chord is 15 ft 7⅞ in from heel to peak and 16 ft 9¼ in with the overhang; the bottom chord is 28 ft.
Web layouts used here
The web members connect the chords. This calculator draws four common layouts. Manufacturers vary the panel points to suit the span and the loads, so treat these as typical layouts, not a design.
| Truss type | Web pieces | Letter: length × count |
|---|---|---|
| King post | 1 | A: 7 ft 4 in ×1 |
| Queen post | 3 | A: 5 ft 0 in ×2; B: 9 ft 4 in ×1 |
| Fink (W) | 4 | A: 4 ft 5⅞ in ×2; B: 8 ft 8¼ in ×2 |
| Howe | 5 | A: 3 ft 10 in ×2; B: 7 ft 4 in ×1; C: 10 ft 1⅝ in ×2 |
- King post: one vertical post from the middle of the bottom chord to the peak. The post is as tall as the truss.
- Queen post: two vertical posts at the third points of the span, joined at the top by a horizontal strut.
- Fink (W): two short diagonals and two long diagonals that make a W. The webs meet the bottom chord at the third points; the short ones reach the middle of each top chord and the long ones reach the peak.
- Howe: vertical posts at the quarter points and the center, plus a diagonal from the foot of each quarter-point post up to the peak.
Truss height and top chord by pitch
For a 24 ft span with no heel or overhang, so the numbers are easy to scale:
| Pitch | Angle | Height at the peak | Top chord, each side |
|---|---|---|---|
| 3/12 | 14.0° | 3 ft 0 in | 12 ft 4⅜ in |
| 4/12 | 18.4° | 4 ft 0 in | 12 ft 7¾ in |
| 5/12 | 22.6° | 5 ft 0 in | 13 ft 0 in |
| 6/12 | 26.6° | 6 ft 0 in | 13 ft 5 in |
| 7/12 | 30.3° | 7 ft 0 in | 13 ft 10¾ in |
| 8/12 | 33.7° | 8 ft 0 in | 14 ft 5⅛ in |
| 9/12 | 36.9° | 9 ft 0 in | 15 ft 0 in |
| 10/12 | 39.8° | 10 ft 0 in | 15 ft 7½ in |
| 12/12 | 45.0° | 12 ft 0 in | 16 ft 11⅝ in |
The top chord per foot of run matches the rafter table printed on framing squares (for example 13.42 inches at 6/12). The rafter calculator gives the same length for a stick-framed roof.
What this does not do
It does not design a truss. Chord and web lumber size and grade, connector plates, bracing, bearing, spacing and uplift all depend on the loads and the local code, and they are set by the truss designer. Ask a truss manufacturer for stamped engineering drawings, and have an engineer or your building department confirm what applies to your project.
Frequently asked questions
How do you calculate roof truss height?
Multiply half the span by the pitch over 12, then add the heel height. A 28 ft span at 6/12 has a rise of 14 × 6 ÷ 12 = 7 ft 0 in; with a 4 inch heel the truss is 7 ft 4 in high at the peak.
How long is the top chord of a truss?
Half the span times the pitch multiplier, plus the overhang times the same multiplier. At 6/12 the multiplier is 1.1180, so a 14 ft run is 15 ft 7⅞ in.
What is heel height?
The vertical depth of the truss at the bearing point, from the underside of the bottom chord to the top of the top chord. A raised heel leaves room for insulation above the wall. In this calculator it simply adds to the height at the peak.
How do I find the web member lengths?
Each web is the straight line between two points on the chords, so its length is the square root of the horizontal distance squared plus the height difference squared. In the Fink layout for the default truss the short web is 4 ft 5⅞ in and the long web is 8 ft 8¼ in.
Can I build my own trusses from these numbers?
These numbers are for layout and for checking a drawing. A structural truss has to be engineered for the loads, span and code where you live. Most trusses are built in a factory from stamped drawings, so ask a truss manufacturer.
Which truss type should I use?
That is a design decision for the truss manufacturer or an engineer, who will pick the layout for your span and loads. This calculator only shows the dimensions of four common layouts.
Related
Other roofing calculators
Sources
- Swanson Tool: Roof pitch reference (rafter length per foot of run) (checked Nov 12, 2026)
- Wikipedia: Truss (king post and queen post trusses) (checked Nov 12, 2026)