Pergola Calculator

Overview

Creates a preliminary freestanding pergola takeoff for posts, beams, rafters, optional purlins, footings, and connectors.

Assumptions

• Four corner posts are used, with two intermediate posts if length exceeds 16 ft.
• Rafters are spaced from the entered on-center value.

Worked example

For a 12-ft length at 20-in rafter spacing, ceil(144 ÷ 20) + 1 = 9 rafters; a 10-ft width gives 12-ft rafters after the two 1-ft overhangs.

Common mistakes

• Treating a decorative pergola as exempt from wind and snow loads.
• Not checking post footing depth for local frost conditions.

Limitations

It does not engineer uplift, lateral bracing, beam spans, shade coverings, or attachments.

Safety and local requirements

Check permits, property setbacks, underground utilities, and overhead lines before construction.

Sources

• International Code Council — code reference background
• OSHA — Landscaping and Horticulture