Registration numbers are one of the few things on your boat that a law enforcement officer can check from 100 yards away. Get them wrong (too small, a fancy font, missing spaces, wrong spot) and it's an easy reason to be stopped. The rules are short and clear, so here they are in plain English.
Who needs registration numbers?
Under 33 CFR 173.15, a vessel covered by the federal numbering rules can't be used unless it has a number issued on a certificate of number by its state of principal operation, and that number is displayed as described in 33 CFR 173.27. In practice, that covers most motorized recreational boats that aren't federally documented. Many states also require numbers on some non-motorized boats, such as sailboats, and states differ on this. Check our registration rules by state page.
The federal display rule: 33 CFR 173.27
The federal rule says each number must:
- Be painted on or permanently attached to each side of the forward half of the vessel. Both sides, in the front half. The transom doesn't count.
- Be in plain vertical block characters of not less than 3 inches in height. No script, italics, slanted, outlined-only or decorative fonts.
- Contrast with the color of the background and be distinctly visible and legible.
- Have spaces or hyphens between the letter and number groups, equal to the width of a letter other than "I" or a number other than "1."
- Read from left to right on both sides of the boat.
The rule's own examples are DC 5678 EF and DC-5678-EF. Note that the separator is as wide as a full character. A tiny gap or a skinny hyphen doesn't meet the rule.
Size: at least 3 inches tall
The 3-inch minimum applies to the characters' height. Taller is fine and often reads better on bigger boats. What matters just as much is the style: "plain vertical block characters" means a simple, upright, sans-serif style with even stroke widths. A slanted "sporty" font at 4 inches still fails the rule because it isn't vertical.
Spacing: the most common mistake
Most registration numbers have three groups: the state prefix, the number, and the suffix letters (for example, FL 3391 BK). Between each group, you need a space or hyphen equal to the width of a letter (other than "I") or a number (other than "1"). Practical tips:
- Lay out the full number on the hull with tape before peeling any backing.
- Use a letter like "B" or a number like "3" from your set as a spacer to check each gap.
- Keep the spacing between characters within a group even and tighter than the gaps between groups. The groups should be obvious at a glance.
Placement: forward half, both sides
- Put the numbers on each side of the forward half of the boat, where they're clearly visible. Most boaters center them on the bow flare, above the waterline and below the rub rail.
- Keep them level and at the same height on both sides.
- Numbers must read left to right on both sides. Don't mirror them on the starboard side.
- Backing plates: If your boat is shaped so a number on the hull or superstructure wouldn't be easily visible (some inflatables and pontoons, for example), 33 CFR 173.27(c) requires the number on a backing plate attached to the forward half so it's visible from each side.
- Tenders: For tenders exempted under 33 CFR 173.13, the number carries a suffix, with a space or hyphen before it, for example DC 5678 EF 1.
- Dealers and manufacturers testing or demonstrating a boat may use removable plates (173.27(b)). That exception doesn't apply to private owners.
The validation decal
Most states also issue a validation decal (sticker) each registration period. Federal rules at 33 CFR 174.15 require states that use decals to have them displayed within 6 inches of the registration number. Whether it goes before or after the number, and on one or both sides, depends on your state. That's the detail people most often get wrong, so check your state on our state-by-state rules page. Leave room for the decal when you lay out your numbers.
Carry the certificate, too
Displaying the number isn't the only requirement. Under 33 CFR 173.21, you must have a valid certificate of number aboard when operating. Since a 2024 amendment, the federal rule allows it in hard copy or digital form. Some states have their own rules on this, so check yours. It's also on our boater checklists.
What about documented boats?
Boats documented with the U.S. Coast Guard follow different marking rules. Under 46 CFR 67.123, a boat documented exclusively for recreation must show its name and hailing port together on a clearly visible exterior part of the hull, in letters at least 4 inches high. The official number is marked on an interior structural part of the hull (46 CFR 67.121). Some states still require documented boats used in the state to carry a validation decal, so check with your state agency. Our lettering size guide explains which of our sizes meet the 4-inch minimum.
Quick compliance checklist
- ☐ Number on both sides of the forward half
- ☐ Plain vertical block characters, 3" or taller
- ☐ Strong contrast with the hull color
- ☐ Letter-width spaces or hyphens between groups
- ☐ Reads left to right on both sides
- ☐ Current decal within 6", placed the way your state requires
- ☐ Certificate of number aboard
Replacing faded or peeling numbers
Faded, cracked or missing characters can make your number hard to read, and the rule requires it to be "distinctly visible and legible." If you're replacing them, see how to remove old lettering without damaging your hull, and have the new set ready before you peel the old one.
Get compliant registration numbers
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Boat Registration Numbers Custom Color Registration Numbers Rules by State
This article summarizes federal regulations and is not legal advice. States may add requirements, so check with your state boating agency.
Sources
- 33 CFR 173.27, Numbers: display; size; color, via eCFR.
- 33 CFR 173.15 and 173.21, via eCFR Part 173.
- 33 CFR 174.15, Validation stickers, via eCFR.
- 46 CFR 67.121 and 67.123, via eCFR Part 67, Subpart I.
- State rules: boater-education handbooks on boat-ed.com and state agency sites. See our state rules page. All sources checked October 8, 2026.