Pergola Rafter Size Calculator

2x4s are generally too small for main rafters unless the span is very short (under 6 feet) or they are used as top slats (purlins). 2x6 is the typical minimum for structural stability and visual appeal.

Yes. Cedar and Redwood are softer woods. While rot-resistant, they are not as strong structurally as Pressure Treated Pine or Douglas Fir, meaning they require shorter spans or larger board sizes.

Clear span is the horizontal distance between the inside faces of the supports (beams or posts). It does not include the overhang or the width of the beams themselves.

If both work structurally, 2x8 is cheaper, but 2x10 looks more robust on larger pergolas (over 12x12). For spans over 12 feet, 2x8 is often the minimum requirement, making 2x10 a safer choice.

For a pergola with no roof load (light load), a 2x6 can typically span 10 to 12 feet depending on the wood species and spacing. Adding a roof covering reduces this max span significantly.

Yes. Beams carry the weight of all the rafters. Beams usually need to be doubled up (e.g., two 2x8s or two 2x10s) and are often one size larger than the rafters for visual balance.

Yes. Wider spacing (e.g., 24" O.C.) puts more load on each individual rafter, often requiring a larger board size compared to tighter spacing (e.g., 12" O.C.).

Absolutely. Pressure treated Southern Yellow Pine is very strong and rot-resistant, making it ideal for structural parts. You can stain or paint it to look like cedar.