Boat Registration Number Size & Spacing Checker
Type your registration number, pick your hull colour, and this checks it against every part of the federal rule — then tells you how wide the finished set will be so you can measure before you order.
The federal rule, in full. Under 33 CFR 173.27, a registration number must:
- be painted on or permanently attached to each side of the forward half of the vessel;
- be in plain vertical block characters of not less than 3 inches in height;
- contrast with the colour of the background and be distinctly visible and legible;
- have spaces or hyphens between the letter and number groupings equal to the width of a letter other than “I” or a number other than “1” — so TX 1234 AB, not TX1234AB;
- read from left to right.
The two things this catches most
No spacing. People order TX1234AB because that is how it is printed on some cards. The rule wants a gap about one character wide between the letter and number groups. We pre-space every set correctly, but if you are cutting your own or buying loose characters, this is the one that fails an inspection.
No contrast. There is no required colour, but the characters must contrast with the background and be distinctly visible. White on white is the classic failure — and it happens because white vinyl is the default on most cheap sets.
Measuring your hull first
You need a flat run on the forward half of the hull, above the waterline, long enough for the width this tool gives you, and tall enough to clear your character height with a little margin. Watch out for rub rails, strakes and rivet lines — vinyl will not bridge a hard edge and stay stuck. On a ribbed aluminium hull, keep the whole set between two ribs.
Questions people actually ask
How tall do boat registration numbers have to be?
Not less than 3 inches in height, in plain vertical block characters. Federal rule, every state. Taller is always legal.
Do boat registration numbers have to be a certain colour?
No specific colour is required, but the characters must contrast with the colour of the background and be distinctly visible and legible. White numbers on a white hull fail that test.
Do I need a space or a hyphen in my boat number?
Yes - a space or hyphen equal to the width of a letter other than 'I' or a number other than '1', between the letter and number groupings. So TX 1234 AB.
How wide will my registration numbers be?
Roughly 0.6 times the character height per character, plus the spaces. A six-character number at 3 inches finishes about 13-15 inches wide. The tool above calculates it for your exact number.