How to Measure a Bullnose Corner Guard

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What is a Bullnose Corner / Corner Guard?

  • A bullnose corner is a rounded or curved exterior edge (as opposed to a sharp 90° corner).
  • A bullnose corner guard is a protective strip (often metal, plastic, vinyl, or other material) shaped to match that rounded edge, to shield it from knocks, scuffs, or impact damage.
  • To order or fabricate one correctly, you usually need two key measurements:
     1. The radius of the rounded corner
     2. The width / wing length (i.e. how far the guard extends along each wall face)

The images above show how the radius and wing width relate.

Tools You’ll Need

  • Tape measure (steel or stiff, so it can lay straight)
  • Straightedge or ruler or framing square
  • Pencil / marker
  • Optional: a flexible ruler or small template, especially if the curve is gentle

Step 1: Measure the Radius of the Rounded Corner

The radius is the distance from the center of the curve to the curved surface (or equivalently, from the start of the curve to the “inside” angle). Here’s how:

  1. Place two straight boards, rulers, or framing square edges flush (tight) against each of the adjoining flat wall surfaces that meet at the corner (i.e. on the two “faces” leading into the curve).
  2. Where those two straight edges meet, that point is the “inside corner” point as though the corner were sharp (even though it’s rounded).
  3. From that inside corner point, measure outward to the point where the rounded curve begins (i.e. the tangent point of the curve). That distance is the radius. (In other words: you measure from the inside corner to where your straightedge no longer touches the wall because the curve begins.)
  4. If the curve is shallow and you can’t see the tangent easily, you may trace or mark a few points and approximate, or use a flexible ruler or template to match.

The image below (top left in the carousel) shows this method visually.

Note: Some corner guard vendors may refer to “radius” differently (e.g. centerline vs face of guard), so double-check their specification definitions.

Step 2: Measure the Wing Width / Coverage

After obtaining the radius, you need to know how wide (how far along each flat wall) the corner guard should extend.

  • Imagine the guard as having two “wings” that lie flat on the adjoining wall faces, meeting in a rounded center.
  • Measure the distance from the outer edge of one wing across the curved section to the outer edge of the other wing. This gives the total width required.
  • Often, each “wing” is symmetric, so you might just need half the total width (one wing) if both sides are identical.

Some manufacturers refer to the wings as the “legs,” “sides,” or “faces” of the guard. The width isn’t the same as the radius — the guard’s width must cover enough of the wall on each side to attach securely. The image below (top right in the carousel) illustrates how radius and width differ.

Step 3: Measure the Height (if applicable)

If your corner guard runs vertically (e.g. from floor to ceiling, or from baseboard to ceiling), also measure the vertical height:

  • From the bottom point (e.g. floor, base, or where the curve ends) to the top where you want the guard to terminate.
  • If the guard is segmented or will be cut, account for any overlaps or joints.

Step 4: Double-Check & Add Tolerances

  • Re-measure each dimension (radius, width, height) to verify.
  • Add a small tolerance (e.g. 1/16" or 1–2 mm) to account for slight misalignments or wall irregularities.
  • If using adhesive or fasteners, confirm how much extra wing is needed for mounting.
  • If ordering from a vendor, verify their measurement conventions (some vendors measure to the inside of the guard material, others to the outer face).

Example Walk-Through

Let’s do a small illustrative example:

  • Suppose a wall corner is rounded with radius = ¾″ (0.75 in).
  • You decide the guard should extend 2″ out from the curve on each side (i.e. each wing). Then the total width = 2″ + (arc width) + 2″ (wings) — often vendors will simplify and say “2″ wings, radius ¾″.”
  • Height required = e.g. 36″ up from baseboard.
  • So you’d order a bullnose guard with: radius = ¾″, wing width = 2″ (or total width 4 + curvature), height = 36″.

Tips & Common Pitfalls

  • Walls may not be perfectly plumb — slight deviations in wall or curve can affect fit.
  • The curve may not be a perfect circular arc (some are elliptical or irregular) — in that case, approximate or sample with a template before final ordering.
  • Always check vendor’s “radius” definition (some use profile radius, centerline radius, face radius, etc.).
  • Ensure the corner guard material thickness is considered (if thick, it may slightly change effective dimensions).
  • For very large radii (gentle curves), use a flexible ruler or bendable metal strip to trace the curve and measure multiple points.

 

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