Do not use one number for two different questions
Physical support length helps you plan how much of the kayak is supported by the bed, an open tailgate or a load-support device. Unsupported length is the kayak length minus that entered support. It is a setup measurement, not automatically the legal rear projection.
Legal rear projection starts at a state-defined vehicle point. California, for example, measures its marker threshold from the taillamps, while other states can describe the rear of the bed, body or vehicle. A bed extender can add support without moving that legal reference point.
Measure the actual truck and kayak
Use the dimensions in front of you instead of relying on a forum post or an unverified trim-level specification. For bed floor support, measure only from the inside front wall to the rear edge of the bed floor. Measure any additional rearward support reach separately, and measure the kayak end to end.
- Do not include an open tailgate in the bed-floor number.
- Record the total additional reach behind the bed floor once, without adding overlapping tailgate and extender lengths; enter zero when there is none.
- Measure the legal projection again from the state-defined point.
- Check wheelbase, last-axle position, overall length and special-cargo exceptions when the official rule uses them.
Choose a setup after the measurement
A bed carry, rear support, bed rack or roof rack changes the physical setup in different ways. It does not automatically change every legal measurement. Confirm hitch compatibility, rated capacity, kayak guidance, anchor points and vehicle limits before selecting equipment.
After dark, do not assume a daytime flag is the complete answer. Covered states can require lamps or reflectors, and the threshold boundary can differ between daytime and darkness.
Compare three layouts for a 12 ft kayak
For this example, the kayak lies straight along a 5 ft 6 in bed floor and its front end starts at the inside front wall. Keep the kayak in the same position while comparing the rear support. These are measured example dimensions, not specifications for a particular truck or a recommendation about support spacing.
| Example layout | Added reach behind bed floor | Length beyond last support |
|---|---|---|
| Bed-floor support only | 0 ft | 12 − 5.5 = 6 ft 6 in |
| Open tailgate providing support | 2 ft | 12 − 5.5 − 2 = 4 ft 6 in |
| Suitable rear support positioned further back | 3 ft in total | 12 − 5.5 − 3 = 3 ft 6 in |
- The third row uses 3 ft of total extra reach, not 2 ft of tailgate plus a second overlapping 3 ft dimension.
- Adding support does not move the kayak's rear endpoint. Re-measure the legal projection from the state-defined origin.
- Length beyond the last support does not describe contact between supports or establish suitable hull support, load distribution or capacity.
This example fills physical dimensions only. The calculator's prefilled legal projection is an unrelated sample, not a measurement supplied by this example. Replace it with a measurement from the selected rule's origin.
Open the 12 ft example and enter your legal projection →Choose between bed carry, rear support and a rack
Start with the truck and kayak manuals, then compare how each layout supports this particular hull. A shorter unsupported length alone is not proof that a layout is suitable. If the instructions or mounting limits do not resolve a proposed layout, choose another transport arrangement before buying equipment.
| Layout | What to resolve before choosing it |
|---|---|
| Bed and open tailgate | Can the specified hull support points be used, and do the tailgate, bed and anchor limits cover the loaded arrangement? |
| Hitch-mounted rear support | Will the installed height and reach support the hull as instructed, with compatible receiver, clearance and rated mounting? |
| Bed rack or roof rack | Check rack spacing, attachment, vehicle roof/bed limits and loading access. Elevated cargo is outside this flat-bed calculator's simple geometry. |
CHECK YOUR NUMBERS
Turn the measurements into a state-specific review.
Enter the physical support length and the state-defined legal projection separately. The result keeps marker rules, projection limits and manual checks distinct.
Measure my setup →Continue planning the load
Read the covered state rules
Frequently asked questions
Does lowering the tailgate reduce legal overhang?
It increases physical support, but it only changes a legal measurement when the applicable rule actually uses the tailgate or support edge as its reference point.
Does a truck-bed extender make the load legal?
No product can make that promise. An extender may add support, but you must separately check projection, marker, total-length, axle, vehicle and permit rules.
Can I use the truck's advertised bed length?
Use a direct measurement for the actual configuration. Advertised dimensions can vary by model, trim, measurement method and tailgate position.
Can I put the kayak diagonally to make it fit?
Diagonal placement changes the rearward projection and can create side projection. The calculator does not model that angle or the hull's support contacts. Measure the loaded rear and sides directly and review the kayak's transport instructions.
Is there a universal percentage of kayak that must stay in the bed?
Overhangers does not apply a universal support percentage. Hull construction, approved contact points, load distribution and vehicle/equipment limits must come from the applicable manufacturers. The state overhang rule answers a separate question.
OFFICIAL SOURCES
Rule information was last checked on Sep 8, 2026. Official pages control if this guide and the current law differ.
California Vehicle Code § 24604 · flags and lights ↗Texas Transportation Code § 621.206 ↗Texas Transportation Code § 547.382 ↗N.C. General Statutes § 20-117 ↗Washington RCW 46.37.140 ↗California Vehicle Code § 35410 · rear projection ↗Texas Transportation Code § 547.302 · lighting times ↗N.C. General Statutes § 20-116 · dimensions and loading ↗Washington RCW 46.44.034 ↗Washington RCW 46.37.020 · lighting times ↗