Enter the length and width of the building, the roof pitch and the truss spacing. The calculator tells you how many trusses you need, the height at the peak, the top chord length and the total cost.
Cost
Trusses are engineered by the truss maker for your loads. Use this to plan and compare quotes.
How many trusses do I need?
- Trusses = building length in inches ÷ spacing, rounded up, plus 1
- Most roof trusses are set 24 inches on center.
- The count includes the two gable-end trusses. These are often a different type with vertical studs for sheathing, so tell your truss supplier.
Worked example
A building 40 ft long and 24 ft wide, with a 6/12 roof, trusses 24 inches on center and a 12 inch overhang:
- Trusses: 40 × 12 ÷ 24 = 20, plus 1 = 21 trusses
- Height at the peak: 12 × 6 ÷ 12 = 6 ft above the bottom chord
- Top chord, each side: (12 ft + 1 ft overhang) × 1.118 = 14 ft 6⅜ in
Common truss types
- Fink (W) truss: the most common for houses and garages. The calculator’s drawing shows this shape.
- Scissor truss: a sloped bottom chord for vaulted ceilings.
- Attic truss: leaves an open room in the middle of the roof.
- Gambrel truss: the barn-style roof with two slopes on each side.
- Mono truss: a single slope, for lean-tos and additions.
The count works the same way for all of them. Peak height and chord lengths here are for a standard gable roof.
Trusses or rafters?
Trusses are factory-built, quick to install and can span wide buildings without interior walls. Rafters are cut on site and leave open attic space. For rafters, use the rafter calculator.
Frequently asked questions
How many trusses do I need for a 40 ft building?
At 24 inches on center, 21 trusses. At 16 inches on center, 31.
How far apart should roof trusses be?
Usually 24 inches on center. Your truss supplier designs them for the spacing, span and loads in your area.
How tall is a truss?
For a gable truss, the height at the peak is half the span × the pitch ÷ 12. A 24 ft span at 6/12 is 6 ft tall.
How much do roof trusses cost?
Prices vary with span, pitch, type and region. Get a quote from a truss supplier and enter the price per truss above for a total.
Can I build my own trusses?
In many areas, trusses must be engineered and stamped. Check with your building department before building them yourself.
Results are for planning. Trusses are designed by the truss maker for your loads. See How We Calculate for the formulas we use.
