Simple Rabbeted Miter Frame Measurements

The simplest way to determine what length your pieces need to be cut for miter frames using a rabbet!

Have you have found yourself starting to cut pieces for a simple miter frame and you realize that you forgot to factor in the width of the board or the depth and height of the rabbet? I definitely have!

It seems that despite having taken (and passed) calculus…I forget how to do simple math. That’s why I wanted to document a SUPER SIMPLE way to determine how long the pieces of a miter frame should be depending on a few basic measurements.

Board Measurements

Easily calculate long edge and short edge based on intended length of art

If you want to make a square frame for a 5″ x 5″ piece of art, you will need to know how long the total piece will be. When you add a rabbet to a frame you should know:

Measurements to Know

Board Width
Board Thickness*
Intended Length of Artwork you’ll be framing (in the example, 5″)
Rabbet Depth (your choice, I often go with .25″)
Rabbet Width (your choice, I often go with .25″)

*Thickness of the board doesn’t effect the math, as I’ll show later

Measurements to Find Out

Long Edge = Length of art + (Board Width x 2) – (Rabbet Depth + Rabbet Width)

Short Edge = Length of art – (Rabbet Depth + Rabbet Width)

$Rabbeted Miter Frame Calculations$

Let’s do the math

$Example Math$

Back to the 5″ x 5″ artwork I want to frame. Let’s say I have a 2″ wide board and plan to cut a .25″ depth and .25″ width rabbet.

Each board will have to be 8.5″ long to account for th 45° miter cut on the 2″ wide board.

*Flub up: Before I started using SketchUp and using this formula, I often would cut the SHORT Edge to be the length of the artwork. I’d cut the rabbet after I did my miter cuts and would end up needing to recut all 4 pieces of the frame.

Thickness of the board does not matter

Whether your board is .75″ thick or 2″ thick, it won’t impact the math here. Neither of the formulas to figure out the final long edge of the board or the short edge of the board require even knowing the thickness of the board! See the image below.

Wider boards will end up having longer final lengths but the short edge will remain the same

Using the same rabbet depth and width and plan to use the same art piece will end up having vastly different lengths, depending on the width of the board. See examples below: three options to frame a 5″ x 5″ piece of artwork using a .25″ deep and .25″ wide rabbet.

1″ wide board

2″ wide board

3″ wide board.

And…that’s it! These graphics may seem overkill or seem to overcomplicate, but visually seeing the various parts of the board and using some simple math has helped me a lot!