Off the shelf pre cut picture frames usually have mat boards with openings that are half an inch smaller than the intended picture size.
Photograph to mat size ratio.
This ratio also known as the golden section golden mean golden number divine proportion divine section etc has been known since antiquity.
Leaving the size at around 3mm makes the picture frame a little larger than the art or window mat being framed.
Perhaps more important than the photograph to frame ratio is the frame to mat ratio.
The majority seem to choose the middle window mat ratio of 1 64.
As a general rule your mat should always be 1 5 times as wide as your frame or wider.
And the reason why this is so is because the middle window mat ratio is the closest one to the golden ratio of 1 618.
The most common size for a photo is 4r or 4 inches by 6 inches typically because it s not too small and not too big.
Some common 1 1 ratios are an 8 x 8 inch photo a 1080 x 1080 pixel image or typically any profile picture template on social media sites think facebook.
For example a 16x20 inch frame including a mat purchased for use with 11x14 prints or photographs will have an actual window opening somewhere in the neighborhood of 10 1 2 x 13 1 2 inches.
Whenever possible avoid pairing a mat with a frame the same size or larger.
This clearance makes the assembly process much easier when fitting up picture frames.
A 1 1 ratio means that an image s width and height are equal creating a square.
The aspect ratio of the photo print is 2 by 3 suitable for photos taken on majority of digital cameras and phone cameras.