How to Measure Baseboard Heaters with Corners

Measuring for Baseboarders• replacement covers is straightforward until you’re backed into a corner,--literally. Then you may run into a few questions and a couple of terms you might not have heard before.

Come with us on a walkthrough of baseboard heater corners. You’ll be an expert in no time.

Things to Know about Baseboard Heater Corners

All corners fit into a couple of categories: the angle of the corner and which direction the corner points. Here’s what you need to know.


The 90-degree corner is the most typical type of corner encountered, as many corners in homes or offices form right angles. These corners typically resemble the letter L.

The other angle found in structures are 135-degree corners. These are much less common than 90-degree corners and are usually found at bay window placements or other “bump-out” type architecture.


Inside corners are those that point away from the room. These are the four corners you find in any standard square room. The corners point away from the center of the room.

In contrast, outside corners angle toward the room. You might see this in an open format space where, for instance, a kitchen connects to a dining room. A wall can provide partial separation in an area even though the room is not completely enclosed. The result is a corner that juts out into the space, or points into the room.

Corner of a room with white baseboard heater.

How to Measure Baseboard Heater Covers for Corners

Now that you’ve identified what type of corner you’re dealing with, measuring is easy as pie. Here’s what you do.


For 90-Degree Inside Corners

  1. Remove existing endcaps and cover panels from the heater.
  2. Measure from the pipe at the far end all the way to the wall.
  3. Subtract 3 inches from this measurement.

Repeat the measurement process for the unit on the opposite wall, following the same steps.

Diagram of how to measure 90 degree inside corner baseboard heater covers.

When dealing with more than one 90-degree inside corner for a single heater unit (forming a U shape), for the longest wall, measure from wall to wall and subtract a total of 6 inches. For the shorter walls, measure from the far end all the way to the wall and subtract 3. Repeat for both short walls.

For 135-Degree Inside Corners

  1. Remove the existing endcaps and front panels.
  2. It is best to measure from where the front plates will meet—usually located 2.5-3” out from the backplate/wall.
  3. No deductions are necessary.

Diagram of how to measure 135 degree inside corner baseboard heater covers.

For 90-Degree and 135-Degree Outside Corners

  1. Remove end caps and front panels.
  2. Measure from the far end of the heater to the point where the two walls meet at the outside corner.
  3. No deduction of 3 inches is necessary since the outside corner piece attaches differently from the inside corner piece. The outside corner piece extends beyond the wall junction and clips to the end of the panels.

Diagram of how to measure 90 degree outside corner baseboard heater covers.

For more details, see our measuring guide.


More Questions?

Have more questions about baseboard heater corners? Visit our corner FAQs to find everything from style selection to installation.