Arbor & Trellis Calculator

A 4 ft wide, 7 ft tall arbor needs two 9 ft posts and 9 slats — enter your arbor's width, height, and post count to get lumber lengths and slat count.

Post length

9 ft

Beam length

4 ft

Slats

9

  • Posts (9ft)

    2 pcs

  • Beam (4ft)

    1 board

  • Lattice / slats

    9 pcs
Enter your local prices to see an estimated cost.

How we calculate this

Post length = height + embed depth (24 in by default, converted to feet). Beam length equals the arbor's width. Slats = width (in inches) ÷ slat spacing, rounded up, plus one so there's a slat at both ends. This covers material quantities only — it's not a structural load calculation, so check span tables or a pro for anything load-bearing.

Estimates only. Check local codes and product labels. Read our full disclaimer.

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