Aircraft N-Number Size Requirements: What 14 CFR 45.29 Says
Compliance reference · Last verified 19 September 2026
Short answer
For most fixed-wing aircraft, N-number characters have to be at least 12 inches high. Two exceptions allow smaller marks: 3 inches for gliders and for many experimental, amateur-built, exhibition and light-sport aircraft with a maximum cruise speed of 180 knots or less, and 2 inches for some older aircraft until they are repainted. The rule is 14 CFR 45.29.
The 12-inch rule
Under 14 CFR 45.29(b)(1), marks on fixed-wing aircraft are at least 12 inches high. That covers most certificated aircraft: a standard-category Cessna, Piper, Beech or Cirrus with a fresh paint job gets 12-inch marks.
When 3 inches is allowed
Marks at least 3 inches high are allowed on:
- gliders
- experimental-certificate aircraft (amateur-built, exhibition, light-sport and similar) with a maximum cruising speed of 180 knots or less, as set out in 14 CFR 45.22 and 45.29
That covers most homebuilts and light-sport aircraft. Faster experimentals over 180 knots go back to 12 inches.
When 2 inches is allowed
Aircraft that were displaying marks at least 2 inches high before November 2, 1981, and aircraft built on or after November 2, 1981 but before January 1, 1983, may keep 2-inch marks. The exception ends when the aircraft is repainted or the marks are restored, repainted or changed. After that, the current size rules apply.
Proportions
Height is only one of the dimensions the rule controls. It also sets proportions based on character height:
| Dimension | Rule | At 12 in high |
|---|---|---|
| Character width | 2/3 of height (M and W may be as wide as they are high) | 8 in |
| Width of the "1" | 1/6 of height | 2 in |
| Stroke thickness | 1/6 of height | 2 in |
| Spacing between characters | At least 1/4 of character width | 2 in or more |
The marks also need to be the same height, width, thickness and spacing on both sides of the aircraft. This is why a generic sticker font often fails. Most typefaces use thinner strokes and narrower letters than the rule allows, so we build every N-number to these proportions before we cut it.
Order a set cut to spec
N-Number Set, Both Sides
Cast vinyl cut to the 45.29 proportions, both sides, shipped. From $95. Experimental Compliance Kit
N-number plus the EXPERIMENTAL marking and placards for homebuilts. $225. Installed at Spokane-area airports
We cut it and apply it on your aircraft. From $195.
Cast vinyl cut to the 45.29 proportions, both sides, shipped. From $95. Experimental Compliance Kit
N-number plus the EXPERIMENTAL marking and placards for homebuilts. $225. Installed at Spokane-area airports
We cut it and apply it on your aircraft. From $195.
Need cockpit and cabin placards too? See the Aircraft Placard Package.
Sources
- 14 CFR 45.29, Size of marks (eCFR)
- 14 CFR 45.22, Exhibition, antique, and other aircraft: Special rules (eCFR)
JZAC Designs is a vinyl shop, not a compliance consultancy. This page summarizes the regulation as published on the date above. For how it applies to your aircraft, check the current eCFR text and ask your FSDO or A&P/IA.