How to Measure an RV Ladder for a Bike Rack: Round, Square or Rectangular Tubing

Quick answer: To check whether an RV ladder can accept a bike-rack mount, measure the ladder tube’s outside diameter—or its outside width and depth if it is square or rectangular—then check the available clearance behind the tube, rung spacing, ladder condition, and the vehicle manufacturer’s load limits.

“RV ladder” sounds like one standard size. It is not. Rear ladders can use round, square, oval, or rectangular tubing, and two ladders that look alike in a photo can measure differently. Taking a few careful measurements before ordering prevents the most common fit problems.

What tools do I need?

• A digital or manual caliper is best for tube diameter and wall-to-wall dimensions.
• A rigid tape measure works when a caliper is not available.
• A straightedge helps check the space behind the ladder tube.
• A phone camera helps document the ladder, mounting feet, hinges, and clearances.

How do I measure round ladder tubing?

Measure straight across the widest part of the tube to get the outside diameter. Do not wrap a flexible tape around the tube and report its circumference unless the mounting instructions specifically ask for circumference.

Measuring round ladder tubing: Wrap a flexible tape measure snugly around the tube where the mounting clamp will sit. The distance around the outside is its circumference. If you don’t have a flexible tape, use a strip of paper, mark where it overlaps, then lay it flat and measure with a ruler. Enter that measurement into this Circumference-to-Diameter Calculator, selecting the correct units, to find your tube’s outside diameter. This method applies to round tubing only.

Take the measurement at the exact height where the rack will mount. Some ladders change tube size or shape near hinges and upper curves.

How do I measure square or rectangular ladder tubing?

Measure both outside dimensions:

• Width: side to side across the face of the tube.
• Depth: front to back, toward the vehicle body.

Do not assume square tubing has equal dimensions. Many RV ladders use rectangular profiles or rounded corners. Record measurements to the nearest 1/16 inch or millimeter, and photograph the caliper or tape in place.

What clearances should I check?

A tube measurement alone does not tell the whole story. Check these areas:

1. Space behind the ladder rail: Measure from the back of the tube to the RV wall, window, trim, or spare-tire cover.
2. Rung spacing: Measure the open vertical distance above and below the proposed mounting point.
3. Left-to-right obstructions: Look for hinges, lights, cameras, handles, license plates, and doors.
4. Bike clearance: Consider handlebars, pedals, tires, and whether a rear door or hatch must remain usable.
5. Road clearance: Nothing should hang where it could contact the road, exhaust, or moving vehicle parts.

Is every RV ladder suitable for carrying bicycles?

No. The ladder and its attachment to the vehicle must be sound and approved for the intended load. Inspect for loose fasteners, corrosion, cracks, bent rails, damaged sealant, or movement at the mounting feet. Check the RV or ladder manufacturer’s documentation for load limits. The lowest-rated part of the system determines the safe limit.

If the ladder is damaged, decorative, removable, or not approved to carry the combined rack and bicycle load, do not mount a bike rack to it.

What photos should I send when asking about fit?

• One full rear view of the vehicle and ladder.
• One straight side view showing ladder-to-body clearance.
• Close-ups of the proposed upper and lower mounting locations.
• A photo of each measurement with the scale visible.
• Photos of hinges, folding sections, unusual bends, or nearby obstructions.

Good photos can answer questions that numbers alone cannot.

Round versus square ladder mounts

A mount designed around round tubing should not automatically be forced onto square or rectangular tubing. The contact surfaces and clamp geometry are different. Bike-Hook is developing ladder-mount solutions with professional hardware selected for the actual tube profile. Read more about the reasoning in Why We Chose Professional Truss Clamps.

For an overview of the current ladder system, see the Bike-Hook Ladder Mount System and Turn Your RV Ladder Into a Removable Bike Rack.

Measurement checklist

• Tube shape
• Outside diameter, or outside width and depth
• Clearance behind the tube
• Open space above and below the mount
• Ladder and mounting-foot condition
• Manufacturer load rating
• Full-view and close-up photos

Measure first, photograph twice, and ask before ordering if anything looks unusual. That small amount of preparation is far easier than adapting the wrong hardware later.

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