Enter the height of the flag and the width of the flag into the calculator to determine the flag aspect ratio.
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Flag Ratio Formula
The calculator uses three formulas, one per mode.
Ratio mode finds the height-to-width ratio from two measurements:
Ratio = Height : Width
If a ratio is selected and only one dimension is given, the missing side is solved as:
Width = Height * (w / h) Height = Width * (h / w)
Pole Size mode recommends a flag size from pole height:
FlagWidth = PoleHeight / D FlagHeight = FlagWidth * (h / w)
U.S. Layout mode uses the official 10:19 proportion:
Width = Height * 1.9 Height = Width / 1.9
- Height (hoist): the vertical edge of the flag, measured along the pole.
- Width (fly): the horizontal edge of the flag, measured away from the pole.
- h : w: the parts of the chosen ratio, such as 2 and 3 in a 2:3 flag.
- PoleHeight: the exposed height of the flagpole above ground or mount.
- D: the divisor for display setting (3, 4, or 5).
The Ratio tab compares two dimensions and reduces them to a clean ratio, or fills in a missing side. The Pole Size tab scales a flag to a pole using a divisor for general, large, or indoor display. The U.S. Layout tab applies the 10:19 standard and returns stripe width, union size, and star spacing.
Common Flag Ratios and Pole Sizing
Most national flags fall into a small set of ratios. Use the table below to identify or pick one.
| Ratio (H:W) | Width ÷ Height | Examples |
|---|---|---|
| 1:1 | 1.000 | Switzerland, Vatican City |
| 2:3 | 1.500 | Germany, France, India |
| 3:5 | 1.667 | Argentina, Germany (state) |
| 10:19 | 1.900 | United States |
| 1:2 | 2.000 | United Kingdom, Australia, Canada |
Pole height drives flag size. The fly should be roughly one quarter the pole height for a standard outdoor display.
| Pole Height | Standard Flag (2:3) | U.S. Flag (10:19) |
|---|---|---|
| 15 ft | 2.5 × 3.75 ft | 2 × 3.8 ft |
| 20 ft | 3.33 × 5 ft | 2.6 × 5 ft |
| 25 ft | 4.17 × 6.25 ft | 3.3 × 6.25 ft |
| 30 ft | 5 × 7.5 ft | 4 × 7.5 ft |
| 40 ft | 6.67 × 10 ft | 5.3 × 10 ft |
| 50 ft | 8.33 × 12.5 ft | 6.6 × 12.5 ft |
Examples and FAQ
Example 1. You have a flag measured at 3 ft hoist by 5 ft fly. Width ÷ height = 1.667, which matches 3:5.
Example 2. You bought a 25 ft pole and want a U.S. flag. Use width = 25 ÷ 4 = 6.25 ft. Height = 6.25 × (10/19) ≈ 3.29 ft. A 3 × 5 ft or 4 × 6 ft flag is the closest stock size.
Why does the U.S. flag use 10:19? Executive Order 10834 set the official proportions in 1959. The same order fixes the union, stripe, and star geometry the calculator returns.
What if my flag does not match a standard ratio? Enter both dimensions in Ratio mode. The calculator finds the closest simple ratio by searching denominators up to 100.
Should the flag width be exactly one quarter of the pole? No. One quarter is a guideline. Use one third for a bolder look on shorter poles, or one fifth indoors and on parade poles.
Does hoist mean height or width? Hoist is the vertical edge next to the pole. Fly is the horizontal edge that flaps in the wind. Flag sizes are usually quoted as hoist × fly.
