1 · Arbor dimensions from use case
2 · Post sizing & burial
Rule of thumb: bury max(24 in, ⅓ of above-grade height). 4×4 posts for openings up to 72 in; 6×6 beyond that or at 10 ft+ height.
3 · Arch top vs flat top planner
Arched top (circular segment)
Flat top
Arch radius formula: R = (rise² + (span/2)²) / (2 × rise). Flat top uses 6-in beam overhang and 8-in rafter spacing.
4 · Side lattice panel sizing
Panels fill the side frames between front and rear posts, with 6 in top/bottom margin. Standard lattice sheet is 4×8 ft; slat option uses vertical 1×2s every 4 in.
5 · Material takeoff
6 · Freestanding stability
Simplified weight-based check (concrete footing weight vs wind overturning moment); soil lateral resistance is not modeled, so it is conservative. PASS requires safety factor ≥ 1.5. Not engineering advice — check local codes.
7 · Cost estimator
Quantities come from the material takeoff; unit prices are ballpark US 2026 and editable below.
Method & sources
Dimensions follow built-product and DIY standards: arbors 7–8 ft tall with 3–4 ft walkway openings (Houzz); manufacturer arched arbors at 102 in tall with 36–72 in openings (ForeverRedwood spec sheet, Cedar Specialties); a classic DIY build on 4×4×8 ft posts set in 8-in-diameter, 2-ft-deep holes (Family Handyman “Classic garden arbor”).
Post burial uses the one-third rule — max(24 in, ⅓ of above-grade height). Arch geometry is an exact circular segment (R = (rise² + (span/2)²)/(2·rise)). A 60-lb concrete bag is taken as 0.45 cu ft; concrete at 150 lb/cu ft. Wind pressure uses the ASCE 7 form P = 0.00256·V² psf with 0.55 solidity for lattice sides plus roof; the stability check is a simplified, conservative weight-based estimate, not structural engineering. Costs are ballpark US 2026 figures — verify local prices.
Frequently asked questions
What is a standard garden arbor size?
Most garden arbors are 7 to 8 feet tall with a clear walkway opening of 36 to 72 inches. A typical garden-entrance arbor is 48 inches wide (55 inches overall), 8 feet tall, and 30 inches deep, which fits one walker plus climbing plants on both sides.
How tall should a garden arbor be?
Make walkway clearance at least 84 inches (7 feet) so tall walkers clear the top beams with plants hanging down. Typical built arbors are 90 to 108 inches: 90 inches for a pathway marker, 96 inches for a garden entrance, and 108 inches for a wedding arch.
How wide should a garden arbor opening be?
Use a 48-inch opening for one person or a garden gate, and a 72-inch opening for two people side by side (a couple at a wedding) or to cover a bench. Add 7 inches for two 4x4 posts to get the overall width: a 48-inch opening is 55 inches overall, a 72-inch opening is 79 inches overall.
How deep should arbor posts be buried?
Use the one-third rule: bury the larger of 24 inches or one-third of the above-grade height. An 8-foot (96-inch) post gets 32 inches of burial, a 9-foot (108-inch) post gets 36 inches, set in a 10-inch-diameter hole with 3 to 4 bags of 60-lb concrete per post.
How do you calculate the arch curve for an arched arbor top?
An arch is a circular segment: radius R = (rise² + (span/2)²) / (2 × rise). For a 55-inch span with a 13.75-inch rise, R = 34.38 inches, the arc is 63.8 inches long, and you can laminate it from 3 two-foot bent segments per arch. Two arches (front and back) need 6 segments total.
How much concrete does each arbor post need?
It depends on hole size and burial depth. A 10-inch-diameter hole with 32 inches of burial holds about 1.23 cubic feet of concrete, which is 3 sixty-pound bags (at 0.45 cubic feet per bag). A taller 108-inch post at 36 inches of burial needs about 4 bags per post.
What is the difference between an arbor, a trellis, and a pergola?
An arbor is a small freestanding archway or gateway structure you walk through, typically 4 to 8 feet wide and 7 to 9 feet tall. A trellis is a flat panel that supports climbing plants and is not a walk-through structure. A pergola is a much larger open-rafter shade structure, usually 8 feet and up in both directions.
How much does it cost to build a garden arbor?
A typical flat-top DIY arbor (48-inch opening, 8 feet tall) costs around $283 in materials at US 2026 ballpark prices: 4 posts ($72), 2 beams ($19), 7 rafters ($29), 7 top lath ($21), lattice sheets ($56), 12 concrete bags ($66), screws ($7), and 4 corner braces ($13). Cedar and stain raise the total.
Will a freestanding garden arbor blow over in the wind?
It can. At 90 mph, wind pressure is 20.74 psf; on an 8-foot-tall arbor that produces about 228 pounds of force and 912 foot-pounds of overturning moment. Standard 12-inch footings resist only 471 foot-pounds (safety factor 0.52), so this calculator recommends 16-inch-diameter footings buried 30 inches deep, which reaches a safety factor of 1.53.