Is There A Certain Size The Rear Tail Lights Have To Be On A Trailer?

Updated 05/06/2026 | Published 05/04/2026

Question:

Hi I’m wondering if there’s a certain size the rear brake lights have to be on a trailer

asked by: Isaac H

Expert Reply:

Hey Isaac, welcome back, and good question. For trailer tail lights it’s not about the physical size as much as it is meeting the lighting requirements.

For trailers in the U.S., the rear brake lights just need to be DOT compliant and visible from a certain distance, typically around 500 feet. There’s no rule that says they have to be a specific size, but they do need to be bright enough, the correct color (red), and properly positioned on the rear of the trailer. Most trailer lights you’ll see are sized the way they are simply because they meet those visibility standards.

As long as you’re using lights that are marked DOT/SAE approved and mounting them at the proper height and spacing, you’re good. So you’ve got some flexibility on size, just don’t go so small that visibility becomes an issue or they don’t meet those standards.

For example, a very common, popular tail light option are the Optronics LED Combination Trailer Tail Lights # TLL160RK. These are submersible LED lights they meet DOT requirements for trailer lights. The lights themselves are 8-1/16" long x 2-7/8" tall x 2-13/16" deep.

What kind of trailer do you have?

expert reply by: Jesse M

Optronics LED Combination Trailer Tail Lights - Submersible - 40 Diodes - Driver and Passenger Side
(click to enlarge)

Isaac H.

5/6/2026

Are there’s taillights dot approved TecNiq Low Profile Stop Tail Turn Light - 15.5" - Clear Lens TN42TR and can I mount them horizontal instead of vertical thank you