Car Trailer Ramp Clearance Calculator
Enter the trailer height, ramp length, loading direction, and the lowest points on the vehicle. The calculator compares the ramp angle with approach and breakover limits, then solves the minimum straight ramp length.
Geometric clearance resultClears geometrically with 1.03 degrees of angle margin.
- Controlling clearance
- Front approach angle
- Angle clearance margin (degrees)
- 1.03
- Additional ramp length needed (in)
- 0
- Minimum ramp surface length (in)
- 108.53
- Ramp angle (degrees)
- 9.59
- Ramp grade
- 16.9%
- Maximum front approach angle (degrees)
- 10.62
- Maximum rear approach angle (degrees)
- 11.31
- Maximum breakover angle (degrees)
- 10.88
Assumes one straight ramp from level ground to a level trailer deck.
How to use this calculator
- Measure deck height vertically from level ground to the top of the trailer deck.
- Measure ramp length along the ramp surface, not across the ground.
- Choose whether the vehicle drives forward or backs onto the trailer.
- Measure the lowest front, rear, and between-axle points before reading the clearance result.
How the ramp clearance check works
This calculator treats the trailer ramp as one straight line from level ground to a level trailer deck. The ramp angle is set by the trailer deck height and the ramp surface length:
ramp angle = asin(deck height / ramp surface length)
The ramp grade uses the horizontal run of that same triangle:
grade = 100 x deck height / sqrt(ramp length^2 - deck height^2)
The vehicle is checked in two ways. First, the calculator compares the ramp angle with the approach angle at the end that enters the ramp first. For forward loading, that is the front low point. For reverse loading, it is the rear low point.
approach angle = atan(low-point clearance / tire-to-low-point distance)
Second, it checks breakover clearance at the lowest point between the axles. Because that point may not be centered, the breakover angle is the sum of the two angles from that low point to the tire contact patches:
breakover angle = atan(belly clearance / belly position) + atan(belly clearance / (wheelbase - belly position))
The controlling angle is the smaller of the selected approach angle and the breakover angle. If the actual ramp angle is steeper than that controlling angle, the vehicle is predicted to scrape at the controlling low point. If the ramp angle exactly matches the limit, the result is only a zero theoretical margin, not useful working clearance.
What changes the answer most
Deck height and ramp length drive the ramp angle. A taller trailer or shorter ramp makes the angle steeper. Vehicle measurements matter just as much: a low splitter far in front of the tire can control forward loading, while an exhaust or crossmember between the axles can control even when both bumpers look safe.
The low point location matters because a centered belly point is not the same as one close to an axle. The centered shortcut is 2 x atan(2 x belly clearance / wheelbase), but the calculator uses the measured off-center position so the result follows the actual car.
What this calculator leaves out
This is a static geometry estimate. It does not model suspension compression, tire deflection, passengers, cargo, uneven pavement, a curved ramp foot, a beavertail, a hinge step, or separate ramp extensions. Those can all change the real clearance. It also does not judge ramp strength, traction, trailer stability, tie-downs, or safe loading procedure.
Worked example
Suppose the trailer deck is 20 inches high and the ramp surface is 120 inches long. The ramp angle is asin(20 / 120), or about 9.59 degrees, and the horizontal run gives a grade of about 16.90%.
The car has 6 inches of front clearance 32 inches ahead of the front tire, 8 inches of rear clearance 40 inches behind the rear tire, a 105 inch wheelbase, and a 5 inch belly low point 52.5 inches behind the front axle. The front approach angle is about 10.62 degrees, the rear approach angle is about 11.31 degrees, and the breakover angle is about 10.89 degrees.
Loaded forward, the front approach angle controls. The ramp is about 1.03 degrees under that limit, so the straight-line geometry clears. The minimum ramp surface length for those measurements is about 108.53 inches, so a 120 inch ramp needs no added length by this model.
Common questions
How do I measure my car's approach angle?
Measure the vertical clearance from the ground to the lowest point ahead of the tire, then measure the horizontal distance from the tire contact point to that low point. The approach angle is the arctangent of clearance divided by distance. If the bodywork is curved, use the lowest point an imaginary straight line from the tire would touch.
How is breakover angle different from ground clearance?
Ground clearance is only the vertical height of a low point. Breakover also depends on where that point sits between the axles. A low point near the middle of a long wheelbase usually needs a shallower ramp than the same clearance near an axle.
Should I drive forward or reverse onto a trailer?
Use the direction that gives the smaller overall risk after considering both approach clearance and how the vehicle will be secured. This calculator compares forward loading with the front low point and reverse loading with the rear low point, but it does not decide weight distribution or safe trailer loading.
How long must a trailer ramp be for a low car?
For one straight ramp, the minimum ramp surface length is deck height divided by the sine of the controlling clearance angle. The controlling angle is whichever is smaller: the loading-end approach angle or the breakover angle. Leave extra length beyond the exact result because a zero margin is not practical clearance.
Will a dovetail or beavertail reduce the required ramp length?
Usually yes, because it reduces the angle change the vehicle sees at the trailer end. This calculator assumes one straight ramp to a level deck, so it does not model a dovetail, beavertail, curved foot, hinge step, or separate ramp extension.