Flagpole Size Calculator

A 3×5 ft flag needs a recommended pole of 20 ft (standard range 15–25 ft) (fly-to-height ratio 1:4; the 1:3–1:5 band is acceptable). The 3×5 is the most common residential flag size, and 20 ft is the most common residential pole — fly it higher and the flag looks undersized; lower and wind load climbs.

A 25 ft pole takes 4×6 to 5×8 ft flags (manufacturer charts). As a rule of thumb, flag fly length should be about one-quarter of pole height (25/4 ≈ 6 ft), and never more than one-third — an oversized flag overloads the pole, halyard and foundation in wind.

Rule of thumb: bury about 10% of the pole height, minimum 2 ft — so a 25 ft pole goes 2.5 ft deep and needs about 6 bags of 80-lb concrete, in firm soil with normal wind exposure. Add 3–6 in of gravel under the sleeve for drainage, use wider holes in sandy soil, and go deeper in high-wind zones. Commercial installs need an engineer, not a rule of thumb.

It depends on hole size: a 20 ft residential pole in a ground sleeve (2 ft deep × 12 in diameter, firm soil) needs about 1.57 cu ft of concrete — about 3 bags of 80-lb concrete. A heavy-duty cube footing for a 30 ft pole (3×3×3 ft) needs about 27 cu ft, or 45 eighty-pound bags. Use the foundation mode above for your exact pole.

Simplified estimate (not engineering): wind pressure q = 0.00256 × V², so at 90 mph q is about 20.7 psf, and a 3×5 ft flag on a 20 ft pole sees roughly 342 lb of force at the top. Pole manufacturers publish max wind ratings with and without a flag — always check the pole's spec sheet for your wind zone, and take the flag down in storms if in doubt.

External halyard (rope outside the pole, tied on a cleat) is cheaper, simpler to replace, and needs about 46 ft of 5/16 in braided polyester for a 20 ft pole. Internal halyard (rope/cable inside, raised with a winch) costs more but is theft-resistant and quieter — the flag can't be lowered without the winch handle. Pick internal for public or commercial sites, external for most homes.

Yes — the US Flag Code (4 USC §6a) says a flag displayed at night should be properly illuminated. For a 25 ft pole, plan on at least one 400+ lumen fixture: one fixture placed 3–5 ft from the base, tilted about 45° to wash the top of the flag. Solar LED spotlights work for most residential poles; use two fixtures on opposite sides for poles over 30 ft.

A typical 20 ft residential install runs about $490: aluminum pole kit $350, 3×5 ft nylon flag $45, concrete $19.50 (3 eighty-pound bags), gravel $15, and a solar LED light $60 — doing the digging yourself. Pro installation adds roughly $400 for poles up to 25 ft; fiberglass poles and internal halyards cost more.

Most homeowners can DIY a 15–25 ft residential pole: dig the hole, set a plumb ground sleeve, pour concrete, wait 24+ hours, then raise the pole. Call 811 before you dig (free utility marking), check HOA rules on height and placement, and hire a pro for poles over 25 ft, rocky soil, or high-wind coastal zones.