EXPERIMENTAL Marking Requirements for Homebuilt and Amateur-Built Aircraft

Compliance reference · Last verified 19 September 2026

The markings are the last thing most builders think about before the airworthiness inspection. Here's what Part 45 asks for, quoted, so you can get it right the first time.

The short answer

  • The word EXPERIMENTAL goes near each entrance to the cabin, cockpit or pilot station.
  • Letters no less than 2 inches and no more than 6 inches high.
  • The same rule covers LIMITED, RESTRICTED and PROVISIONAL aircraft, each with its own word.
  • N-number size: 3 inch minimum for amateur-built, exhibition and light-sport aircraft at 180 knots or less; 12 inch otherwise (14 CFR 45.29).
  • Passenger warning and other placards usually come from your operating limitations, not Part 45. Check yours.

The EXPERIMENTAL marking

From 14 CFR 45.23(b), quoted verbatim:

Except for unmanned aircraft, when marks include only the Roman capital letter “N” and the registration number is displayed on limited, restricted, experimental, or provisionally certificated aircraft, the operator must also display on that aircraft near each entrance to the cabin, cockpit, or pilot station, in letters not less than 2 inches nor more than 6 inches high, the words “limited,” “restricted,” “experimental,” or “provisional,” as applicable.

Things builders ask about:

  • “Near each entrance.” Two doors means two markings. A canopy aircraft typically carries it by the canopy rail or on the fuselage beside the cockpit.
  • Height window. Under 2 inches is too small, and over 6 inches is too big. We usually cut 2 or 3 inches, which reads cleanly without shouting.
  • Color and font. Part 45 doesn't set a color for this word. Pick one that contrasts with the paint so the inspector can see it.

The N-number on an experimental

Registration mark size is in 14 CFR 45.29. The short version for experimentals:

  • At least 3 inches for amateur-built, exhibition and light-sport aircraft with a maximum cruise of 180 knots CAS or less, and for gliders
  • At least 12 inches for faster fixed-wing aircraft
  • Character width 2/3 of height, stroke 1/6 of height, spacing at least 1/4 of character width, the same on both sides

The full rule with every proportion is on our aircraft N-number size requirements page.

Placards

Your operating limitations, issued with your special airworthiness certificate, list the placards your aircraft needs. The passenger warning placard lives there, not in Part 45. Read your limitations and match the wording exactly. We cut placards to whatever text they specify.

A pre-inspection checklist

  • N-number on both sides, at the right height and proportions
  • EXPERIMENTAL near each entrance, 2 to 6 inch letters
  • Every placard your operating limitations call for, in the exact wording
  • Everything contrasting with the paint and firmly attached

Experimental kit

$225

Shipped nationwide

  • N-number, both sides, cut to 45.29 proportions
  • EXPERIMENTAL lettering
  • Placards to your wording
  • Proof before we cut
Order the kit

N-number only

From $95

Shipped nationwide

  • Both sides, cast vinyl
  • 3 inch or 12 inch
  • Pre-masked, one piece per side
N-number set

Placards

From $85

Cockpit and cabin

  • Cut to your operating limitations
  • Matching font and color
Placard package

Nothing is cut until you approve your proof.

Sources

Last verified 19 September 2026 against the current eCFR text. Your operating limitations and your inspector have the final word on your aircraft.

JZAC Designs describes the standards we build to. We are a vinyl shop, not a compliance consultancy, and we do not advise on anyone's own regulatory obligations. Confirm final requirements for your situation with the agency that regulates it.