Flag Size Calculator
Size a flag to your pole so it looks proportional instead of puny or overloaded. Enter pole height in feet and whether it is an in-ground pole or a house-mounted bracket pole; you get the closest standard flag size and the acceptable fly-length range.
Example: with Pole type In-ground flagpole · Pole height / length (ft) 20 → Recommended flag size: 4 ft × 6 ft (closest standard size to the 1/4-1/3 rule).
- Acceptable fly lengthFly length 5.0 to 6.7 ft (1/4 to 1/3 of a 20 ft pole)
- Flag area24 sq ft (4 ft hoist × 6 ft fly)
Computed by the calculator below using its default values. Change any input to see your own numbers.
US flag industry convention: the flag's fly (long side) should be one-quarter to one-third of an in-ground pole's height. House bracket poles of 5-6 ft fly a 2.5 × 4 ft or 3 × 5 ft flag.
The 1/4-to-1/3 rule
Flag makers size flags to poles with one convention: the fly — the flag's long, horizontal dimension — should be at least one-quarter and at most one-third of the pole's height above ground. A 20 ft residential pole therefore wants a fly of 5 to 6.7 ft, and the standard 4 × 6 ft flag sits neatly in that band. Below a quarter, the flag reads as an afterthought; above a third, it visually overwhelms the pole and, more practically, overloads it — wind force grows with flag area, and pole ratings assume conventional sizing.
Standard US retail flags come in fixed sizes (3 × 5, 4 × 6, 5 × 8, 6 × 10, 8 × 12, 10 × 15, 12 × 18, 15 × 25, 20 × 30 ft), so this calculator picks the stock size whose fly lands closest to the middle of your pole's acceptable band.
House poles and flag proportions
A house-mounted bracket pole is a different animal: a 5-6 ft pole set at roughly 45° from a wall bracket. Convention there is a 2.5 × 4 ft or 3 × 5 ft flag — bigger drags on the ground or the house. Note that retail US flags use a 3:5-ish width-to-length ratio, while the official government specification (Executive Order 10834) is 1:1.9. Both fly fine; the retail ratio just looks fuller on short poles.
How it’s calculated
In-ground poles: acceptable fly = pole height ÷ 4 to pole height ÷ 3. The recommended flag is the standard size (3×5, 4×6, 5×8, 6×10, 8×12, 10×15, 12×18, 15×25, 20×30 ft) whose fly is closest to the band midpoint, 7/24 × height (≈ 0.292 × height). House bracket poles: 2.5 × 4 ft for poles up to 5 ft, 3 × 5 ft for 5-6 ft poles. Area = hoist × fly.
This is the flag industry's proportional convention, not a structural rating — in high-wind regions or for poles over ~100 ft, confirm the pole's rated flag area with the manufacturer.
Standard pole-to-flag size chart
| Pole height | Typical flag size |
|---|---|
| 15 ft | 3 × 5 ft |
| 20 ft | 3 × 5 or 4 × 6 ft |
| 25 ft | 4 × 6 or 5 × 8 ft |
| 30-35 ft | 5 × 8 or 6 × 10 ft |
| 40-45 ft | 6 × 10 or 8 × 12 ft |
| 50 ft | 8 × 12 or 10 × 15 ft |
| 60-65 ft | 10 × 15 or 12 × 18 ft |
| 70-80 ft | 12 × 18 or 15 × 25 ft |
US flag manufacturers' published pole-to-flag charts, all built on the fly = 1/4 to 1/3 of pole height convention.
Common mistakes
- Measuring the pole's exposed height plus the buried section — use height above ground only.
- Sizing a house bracket pole like an in-ground pole; a 6 ft bracket pole takes a 3 × 5 ft flag, not a 2 ft flag.
- Going above the 1/3 rule for looks — a too-big flag strains the pole and halyard in wind and wears out faster.
- Forgetting that two flags on one pole add area; drop one size when flying a second flag beneath the first.
Frequently asked questions
What is the formula for flag size from pole height?
Fly length = pole height ÷ 4 at minimum and ÷ 3 at maximum; this calculator targets the midpoint, 7/24 of pole height, then picks the closest standard flag. A 25 ft pole targets about 7.3 ft of fly, so a 5 × 8 ft flag.
What size flag for a 20 ft pole?
A 4 × 6 ft flag is the best proportional fit (fly band 5 to 6.7 ft). A 3 × 5 ft also flies acceptably on 20 ft and is the safer choice in high-wind areas.
What size flag for a house-mounted pole?
The standard 5-6 ft angled bracket pole carries a 2.5 × 4 ft or 3 × 5 ft flag. The 3 × 5 is the most common; go 2.5 × 4 if the mount is low enough that a bigger flag would brush the ground or shrubs.
Why is my flag a 3:5 shape when the official US flag is 1:1.9?
Executive Order 10834 sets 1:1.9 for government flags, but retail flags are made in 3:5-ish proportions because they look fuller and waste less fabric. Both are legitimate ways to fly the flag; this calculator sizes by the fly dimension either way.
Does a bigger flag need a stronger pole?
Yes. Wind load scales with flag area, and pole wall thickness and halyard hardware are rated assuming conventional flag sizes. If you want to exceed the 1/3 rule, check the pole manufacturer's maximum flag area for your wind zone first.