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Roof Truss Calculator

The roof truss calculator is a handy tool that will help you estimate both the rafter length and the number of trusses needed for your roof.

Clear
Top chord length14 ft 6.41 in14.5344 ft including the overhang
Top chord to the peak13 ft 5 inheel to ridge, no tail
Bottom chord24 ftthe full span
Peak height above the bottom chord6 ft 3.5 in6 ft of rise plus 3.5 in of heel
Outer web (×2)8 ft 2.95 in8.2462 ft
Inner web (×2)5 ft 7.88 in5.6569 ft
Lumber per truss80.875 ftchords and webs together
Trusses needed19at 24 in centres over 36 ft
Total lumber1,536.6 ft1,024.4 board feet at 2×4
Roof area965.98 sq ftexcluding overhangs
Slope angle26.565°
Engineeringhave it designedtrusses are engineered assemblies — plate sizes and member grades are not something to estimate

The method

top chord = √(run² + rise²); web layout follows the truss type

Geometry you can work out, loads you should not

The lengths here follow from the span and the pitch, and they are useful for ordering material and checking a drawing. The part that matters structurally — member grades, the size and placement of the connector plates, the bracing — is engineered, and a truss depends on those details completely.

The Fink or W truss is the standard residential form because its webs meet the bottom chord at the third points, which keeps every member short and in either pure tension or pure compression. A king post suits short spans, and a Howe carries more but uses more timber.

Never cut, notch or drill a truss member. Every one is sized for its exact load path, and there is no spare capacity to borrow.