As you type in your dimensions in the fields (in inches), the results will update at the bottom of the calculator.
Glossary of terms:
Picture dimensions: Measure the entire image size which will appear inside the mat (or frame); be sure to include any white space between the image and the mat/frame.
Mat borders: Usually equal all the way around; sometimes the borders are uneven when fitting a new picture in an existing frame, in some cases a drop-bottom is used, where the bottom border is larger than the other three.
Frame width: measured in inches - the width of the frame is used to calculate how many linear feet are required to make the frame. This is the number that is multiplied by the frame price per foot to get the total frame price.
Results: The rabbet is the measurement inside the frame from edge to edge and is usually the same as the mat width and height. Linear feet is the number used as the multiplier for the frame price per foot.