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Pergola Post Spacing Calculator

Estimate how many support posts you need for a rectangular pergola based on maximum beam span.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax
13.12 ft9.84 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Posts needed

8 posts

Check your inputs

This is a general layout planning estimate — final beam sizing and post spacing should be confirmed against your local building code and beam span tables for the actual lumber species, grade, and expected roof/shade structure load.

Posts along each long side
3 posts
Posts along each short side
3 posts

For the dimensions entered, expect a posts needed of 8. Of the working steps, posts along each long side dominates at 3 posts. Moderate confidence — sound arithmetic, but allow for the variation any real site introduces. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Posts are placed at all 4 corners plus intermediate posts along any side exceeding the maximum beam span, spaced no farther apart than the maximum span

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why subtract 4 from the total?
Each of the 4 corner posts is counted once in the 'along length' total and once in the 'along width' total, so subtracting 4 removes that double-count of the shared corner posts.
Does beam size really affect how many posts I need?
Yes significantly — a larger, stronger beam can span farther between posts, meaning fewer posts for the same pergola footprint, while a smaller beam needs more frequent support. Check span tables for your specific beam dimensions.
Should posts be set in concrete?
Most permanent pergola posts are set in concrete footings below the frost line (see the Concrete Bag Calculator and Deck Footing Calculator) for stability against wind and structural loads, similar to deck post footings.