Most of a pergola build is just lumber, but the piece count adds up once you factor in posts, beams, rafters, and purlins. Enter your dimensions to get a count for each component.
Pergola Dimensions
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Scenario: You're building a 12 ft x 10 ft pergola.
Result: You need 4 posts, 2 beams, 10 rafters spaced 16 inches on center along the length, and 16 purlins spaced 8 inches on center along the width.
A standard rectangular pergola uses 4 posts (one at each corner). Add 2 intermediate posts if the span exceeds 12 feet on any side. Extremely large pergolas (over 20 ft) may need additional posts for structural support.
Posts: 6x6 for up to 10 ft height. Beams: 2x8 for spans up to 10 ft, 2x10 for 10-14 ft. Rafters: 2x6 or 2x8 at 16 inch spacing. Purlins/slats: 2x2 or 2x4 at 6-8 inch spacing. Use pressure-treated or cedar for outdoor longevity.
Set posts at least 24 inches deep, or below the frost line in cold climates. Pour a concrete footing around each post (about 2 bags of 80 lb concrete per post) and let it cure 24-48 hours before building the top structure.
Many jurisdictions require a permit for structures over a certain height or attached to the house. Freestanding pergolas under 200 sq ft often don't require one, but rules vary widely. Check with your local building department before starting.
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