Article — Flag Calculator
Flag Calculator: US Flag Dimensions and International Aspect Ratios
The official US Government flag has a hoist-to-fly ratio of exactly 10:19, set by Executive Order 10834 in 1959 and codified in 4 USC § 1. The blue union covers 7 of the 13 stripes vertically and 76% of the hoist horizontally, with 50 stars sized at 4/65 of the hoist.
Most American homes do not fly a 10:19 flag, though. The 3 ft × 5 ft residential flag familiar to porches and front yards uses a 2:3 ratio, which is unregulated and far more common worldwide. The calculator above handles both: pick a ratio, enter either the hoist or fly, and read the matching dimension along with the union, stripe, and star sizes when you select the 10:19 standard.
What this flag calculator does
The calculator solves three related problems. First, given a flag's hoist (height along the pole) and an aspect ratio, it computes the fly (length away from the pole) — or vice versa. Second, when you choose the US Government 10:19 ratio, it returns the union (canton) height and width, the stripe width, and the star diameter, each scaled exactly as 4 USC § 1 requires. Third, it returns the flag's area in both square feet and square meters, useful for ordering fabric.
The input unit toggles between inches, feet, centimeters, and meters. Inches works best for residential and small flags; feet works best for commercial and government flags. The metric units come in handy for international flags or fabric calculations done in metric.
US flag dimensions under 4 USC § 1
Title 4 of the United States Code, Section 1, fixes the proportions of the Stars and Stripes for federal use. Executive Order 10834, signed by President Eisenhower in 1959 after Hawaii became the 50th state, set the modern dimensions. The flag is divided into 13 horizontal stripes (7 red, 6 white) representing the original colonies. The blue canton in the upper-left corner contains 50 white stars in nine rows that alternate between six and five stars.
Each measurement scales as a fixed fraction of the hoist. The fly is 1.9 times the hoist (the 10:19 ratio). The union height is 7/13 of the hoist. The union width is exactly 76% of the hoist. Each stripe is 1/13 of the hoist wide. Each star has a diameter of 4/5 of a stripe, or 4/65 of the hoist. A 10-foot hoist therefore gives a 19-foot fly, a 5.38-foot union height, a 7.6-foot union width, 9.23-inch stripes, and 7.4-inch stars.
Executive Order 10834 also specifies the exact shade of blue and red. Old Glory Blue is Cable No. 70075 (CIE chromaticity coordinates x=0.144, y=0.080); Old Glory Red is Cable No. 70180. The same shades appear on every federally manufactured US flag.
Flag aspect ratios around the world
The 10:19 ratio is unique to the United States Government. Roughly half of the world's national flags use 2:3 — France, Germany, Russia, India, Brazil, and most of Latin America, along with the unofficial US residential flag. Another 20 or so countries use 1:2, including the United Kingdom, Italy, and Denmark, a holdover from British and Scandinavian naval traditions. China and Vietnam use 5:8, somewhere between 2:3 and 10:19.
Two countries fly square (1:1) flags: Switzerland and Vatican City. Qatar holds the record for the widest national flag, with a 11:28 ratio (about 1:2.545). The proportions correlate loosely with regional history: British colonies tended to inherit 1:2, French colonies and post-revolutionary republics tended toward 2:3, and Germanic flags often used 3:5. The 10:19 American ratio was a deliberate choice in 1959 to set Government flags apart from civilian variants.
Choosing a residential flag size
The most common American residential flag is 3 ft by 5 ft, sized in a 2:3 ratio. It fits a standard 6-foot porch flagpole or a 15-foot in-ground pole. The next step up is 4 ft by 6 ft for a 20-foot pole, and 5 ft by 8 ft for a 25- to 30-foot pole. The Department of Veterans Affairs distributes 5 ft by 9.5 ft (1:1.9) casket flags for military burials.
Federal law does not require the 10:19 ratio for civilian flags. The Federal Flag Code (4 USC) outlines display etiquette but does not penalize unofficial proportions. The 2:3 residential standard exists because mass-produced 10:19 flags would be unusually long for most pole heights and tend to wrap on themselves in light wind.
Flagpole-to-flag sizing
The fly should be roughly 25% to 33% of the flagpole height. Below 25% the flag looks lost; above 33% it strains the halyard and can wrap around the pole. A 20-foot residential pole takes a flag with a fly between 5 and 6.7 feet — so 4 ft by 6 ft is the standard match, and 5 ft by 8 ft is the upper end.
15 ft pole 3 x 5 ft flag20 ft pole 4 x 6 ft flag25 ft pole 5 x 8 ft flag30 ft pole 6 x 10 ft flag40 ft pole 8 x 12 ft flag50 ft pole 10 x 15 ft flagCanton, stripes, and stars
The canton — the blue rectangle in the upper-left corner — is the most visually distinctive element of the US flag. It is officially called the "union" because it represents the union of states. Its height is exactly 7/13 of the hoist, meaning it covers seven of the thirteen stripes vertically. Its width is precisely 0.76 of the hoist.
Inside the union, the 50 stars are arranged in nine rows. Rows 1, 3, 5, 7, and 9 contain six stars each (30 total); rows 2, 4, 6, and 8 contain five stars each (20 total). Each star has a diameter equal to 4/5 of a stripe width — which works out to 4/65 of the hoist, about 6.15%. The geometry is exact: a 10-foot hoist makes every star 7.385 inches across.
- 13 stripes represent the original colonies (7 red, 6 white, equal width)
- 50 stars represent the current states, arranged in 9 alternating rows
- Union height = 7/13 of hoist (covers 7 stripes)
- Union width = 0.76 of hoist
- Stripe width = 1/13 of hoist
- Star diameter = 4/5 of stripe = 4/65 of hoist
- Top stripe is always red; bottom stripe is also red
- Union color is Old Glory Blue, Cable No. 70075
Casket flag and special flags
The casket flag — the burial flag draped over the coffin of a deceased veteran — measures 5 ft by 9.5 ft, a 1:1.9 ratio. The Department of Veterans Affairs provides one to the family of every honorably discharged veteran free of charge. Its slightly different proportions from the 10:19 government flag (1:1.9 versus exactly 10:19) reflect the historical Army Quartermaster Corps specification adopted before 1959 and retained for ceremonial continuity.
Other special-purpose US flags include the storm flag (5 ft by 9.5 ft), the post flag (8.95 ft by 17 ft), and the garrison flag — the largest, at 20 ft by 38 ft, flown at military installations on national holidays. All maintain the 10:19 or close-to-1:1.9 proportions consistent with the federal standard.
If a flag is going to be flown around the clock, light it after sunset per 4 USC § 6. The federal flag code requires that an unlit flag be lowered each evening. A solar-powered pole light is the simplest way to comply.
Common flag-sizing mistakes
The most common error is buying a flag too large for its pole. A 5 ft by 8 ft flag on a 15-foot pole nearly drags the ground and tangles in even light wind. The opposite error — undersizing — happens with 25- and 30-foot commercial poles flying 3 ft by 5 ft residential flags that look like postage stamps from the street.
The second error is confusing the 10:19 government ratio with the 2:3 residential ratio. The government version is roughly 27% longer than the residential version for the same hoist. Order a 10:19 flag for a 2:3 pole spread and the proportions will look wrong against neighboring flags.
Always specify hoist before fly when ordering. Most flagpole hardware (snap hooks, halyards) attaches along the hoist edge. Ordering "5 by 8" can be ambiguous; "5-foot hoist, 8-foot fly" leaves no room for error.