Aircraft N Number Size Requirements by Aircraft Type

Aircraft N number size requirements come down to one default and a short list of exceptions. Most airplanes and helicopters must show registration marks at least 12 inches high under 14 CFR 45.29. Gliders, balloons, powered parachutes and certain experimental or antique aircraft may use smaller marks. This is a plain-words summary, not advice, so read the current rule and ask your inspector or local FAA office if unsure.

Who needs 12 inch marks

Fixed-wing aircraft and rotorcraft (helicopters) must show marks at least 12 inches high, with the exceptions below and a repaint exception for some older helicopters in paragraph (b)(3). Any aircraft that flies into an air defense identification zone (an ADIZ or DEWIZ) must show marks at least 12 inches high, temporary or permanent, under paragraph (h). If your aircraft is not clearly named in an exception, treat 12 inches as your size.

Experimental aircraft N number size and the 180 knot condition

Marks of 3 inches are allowed on an aircraft with an experimental airworthiness certificate when it operates as an exhibition aircraft, an amateur-built aircraft, or a former or kit-built light-sport category aircraft, and its maximum cruising speed does not exceed 180 knots CAS, calibrated airspeed (14 CFR 45.29(b)(1)(iii)).

Above 180 knots CAS the exception does not apply. The rule names specific purposes, so if your certificate was issued for a different one, ask the FAA which size applies.

N number height for gliders, balloons and powered parachutes

Gliders may use marks of 3 inches or more. Airships, spherical and non-spherical balloons, powered parachutes and weight-shift-control aircraft must show marks of at least 3 inches (14 CFR 45.29(b)). A 6 inch mark is larger than these cases ask for and smaller than the 12 inch default.

The 2 inch case for antique and exhibition aircraft

14 CFR 45.22(b) lets a small aircraft built at least 30 years ago, or an amateur-built or exhibition experimental aircraft with the same external configuration as one built that long ago, show marks of 2 inches or more on each side of the fuselage or vertical tail surface. The rule has other conditions, so read it first.

Older small marks and repainting

An aircraft whose marks were 2 inches or more before November 1, 1981 may keep them until the aircraft is repainted or the marks are repainted, restored or changed (45.29(b)(1)(i)). After that the 12 inch default applies, unless 45.22(b) fits. If unsure whether a replacement counts as a change, ask the FAA.

Character proportions and spacing

The rule sets the shape of every character, not just its height (45.29(c) to (e)):

• Width: two-thirds of the height.
• The number 1: one-sixth as wide as it is high.
• The letters M and W: may be as wide as they are high.
• Thickness of the lines: one-sixth of the height.
• Space between characters: at least one-quarter of the character width.

Both sides of a fixed-wing aircraft must match.

A worked example: N1234 has no M or W. At 3 inches each character except the 1 is 2 inches wide, the 1 and the line thickness are half an inch, and the gaps are at least half an inch, so the mark runs about 10.5 inches. At 12 inches it runs about 42 inches. That is our own arithmetic at the smallest spacing, so wider gaps, an M or a W make it longer.

Where tail number marks go

Fixed-wing aircraft show the marks horizontally on both sides of the vertical tail, or horizontally on both sides of the fuselage between the wing's trailing edge and the front edge of the horizontal stabilizer (14 CFR 45.25). An aircraft allowed marks of 3 inches may also place them vertically on the tail. Rotorcraft, balloons, airships, powered parachutes and weight-shift aircraft have their own spots in 14 CFR 45.27.

Marks must contrast with the background, be legible and have no ornamentation. They are painted on or affixed by other means that give a similar degree of permanence (45.21). Readily removable material is allowed only in listed cases, such as a temporary registration number.

N number format

U.S. marks are the capital letter N plus the registration number, up to five more characters. The FAA N-number page shows three shapes: all numbers (N10000), one to four numbers and one letter (N1000A), or one to three numbers and two letters (N100AB). The letters I and O are not used, and a number cannot start with zero. Do not apply a new number before the FAA assigns it.

What AC 45-2E says about decals

FAA Advisory Circular 45-2E lists decals among the ways to apply an N number permanently and says not to use tape that can be peeled off. It asks for plain capital Roman style letters without ornamentation and names no typeface. It is guidance, not a regulation, and predates the latest size rule.

Ordering N number decals

Our aircraft N number decals page takes the N number you type and checks it for the FAA format. You pick the aircraft type and a letter height of 2, 3, 6 or 12 inches, and the characters are drawn to the proportions above. They are printed vinyl with a gloss laminate, each piece with a thin border in the background color you pick, so you match it to your paint. Marks up to 6 inches come as one piece per side. A 12 inch mark comes as one piece per character with a half-inch border, and the spacing to use is printed on the order. Every order is a matching pair for both sides.

Prices per pair: $29.99 for 2 or 3 inch marks, $49.99 for 6 inch marks, $89.99 for 12 inch marks.

Our decals are not approved by the FAA, and you are responsible for the size and position on your aircraft. If you are unsure, ask your A&P, inspector or local FAA office. For general steps, see our guides to installing decals on a truck door, applying boat registration numbers and removing truck decals. They are written for trucks and boats, so check your aircraft's finish with your A&P. More decals are in the shop.