Roof Truss Calculator is the fastest calculator a Roof Truss. Just provide a Roof length and a On Center Spacing and you’ll get an Truss Count, instantaneously. Roof Truss Calculator can also quickly determine Truss Count based on Roof length and On Center Spacing expressed in: 1. Meters 2. Centimeters 3. Inches 4. Feet Calculate Roof Truss quickly and as you want.