Boat Trailer Size Calculator
The boat trailer size calculator helps you estimate the recommended trailer length and minimum load capacity based on your boat's length and dry weight. Note: Calculations include a standard 15% weight buffer for fuel, water, and gear.
Additional Information
1. Bunk vs. Roller Trailers
Bunk trailers use carpeted boards to support the hull. They are typically cheaper, require less maintenance, and are great for drive-on loading if you frequent deep boat ramps. Roller trailers use rubber or plastic rollers. They make launching and retrieving much easier at shallow ramps, but provide less continuous support for the hull.
2. Single vs. Tandem Axle
As a general rule, boats weighing over 3,000 lbs (approx. 1,360 kg) or longer than 20 feet (6 meters) should be paired with a tandem (dual) axle trailer. Tandem axles tow straighter, handle blowouts safer, and distribute weight much more effectively.
3. Tongue Weight Matters
Your trailer’s tongue weight (the downward force exerted on the tow vehicle's hitch) should generally be between 5% and 10% of the total loaded trailer weight. Too little tongue weight causes trailer sway; too much limits your vehicle's steering and braking capacity.
Frequently Asked Questions (FAQ)
Why do you add 15% to the dry boat weight?
Manufacturers list the "dry weight" of a boat, which excludes fuel, fresh water, batteries, outboard motors (in some cases), and personal gear. The standard 15% buffer safely accounts for these operational necessities so you don't overload your trailer.
How is the recommended trailer length calculated?
A trailer generally needs to be about 2 feet (or ~0.6 meters) longer than the centerline length of your boat. This provides the necessary clearance for the bow winch stand and ensures your outboard motor or sterndrive doesn't scrape the ground or hit the rear of the tow vehicle during tight turns.
What happens if my trailer capacity is too exact?
Running a trailer at its maximum capacity causes extreme wear on the tires, bearings, and suspension. It is always highly recommended to round up to the next highest capacity rating for safety and longevity.