Choosing the right frame involves more than just matching the size of your photo. If you plan to use a mat (the cardboard border inside the frame), the dimensions of your frame will change significantly. This calculator helps you determine exactly what size frame, glass, and mat opening you need for a professional look.
The Math Behind Frame Sizing
To calculate the correct dimensions, we use the following formulas:
Mat Opening: This is typically 1/4 inch (0.25″) or 1/8 inch (0.125″) smaller than your photo on all sides. This "overlap" ensures the photo doesn't fall through the hole in the mat.
Glass Size (Internal Frame Size): This is the sum of your photo size plus the mat borders, minus the overlap. Formula: Photo Dimension + (Mat Width × 2) - (Overlap × 2).
External Frame Size: This is the total space the frame will occupy on your wall. Formula: Glass Size + (Frame Molding Width × 2).
Example Calculation
If you have an 8×10 inch photo and you want a 2-inch mat border with a 0.75-inch thick frame molding:
Mat Opening: 7.75″ x 9.75″ (using 1/8″ overlap per side).
Glass/Backing Size: 11.75″ x 13.75″. This is the size of the frame you would buy at a store.
Total External Size: 13.25″ x 15.25″. This is the actual footprint on your wall.
Standard Frame Size Chart
Photo Size
Standard Mat Width
Common Frame Size
4″ x 6″
1″ – 2″
6″ x 8″ or 8″ x 10″
5″ x 7″
1.5″ – 2.5″
8″ x 10″ or 11″ x 14″
8″ x 10″
2″ – 3″
11″ x 14″ or 16″ x 20″
function calculateFrameSize() {
var pW = parseFloat(document.getElementById('photoWidth').value);
var pH = parseFloat(document.getElementById('photoHeight').value);
var mW = parseFloat(document.getElementById('matWidth').value) || 0;
var fM = parseFloat(document.getElementById('frameMolding').value) || 0;
var overlap = parseFloat(document.getElementById('overlap').value);
if (isNaN(pW) || isNaN(pH)) {
alert("Please enter valid photo dimensions.");
return;
}
// 1. Mat Opening (The window through which the photo is seen)
var matOpeningW = pW – (overlap * 2);
var matOpeningH = pH – (overlap * 2);
// 2. Glass Size (The internal dimensions of the frame)
// If no mat is used, the glass size is the same as the photo size
var glassW, glassH;
if (mW > 0) {
glassW = matOpeningW + (mW * 2);
glassH = matOpeningH + (mW * 2);
} else {
glassW = pW;
glassH = pH;
}
// 3. External Size (Total footprint on wall)
var extW = glassW + (fM * 2);
var extH = glassH + (fM * 2);
// Display Results
document.getElementById('matOpening').innerHTML = matOpeningW.toFixed(3) + '" x ' + matOpeningH.toFixed(3) + '"';
document.getElementById('glassSize').innerHTML = glassW.toFixed(3) + '" x ' + glassH.toFixed(3) + '"';
document.getElementById('externalSize').innerHTML = extW.toFixed(3) + '" x ' + extH.toFixed(3) + '"';
document.getElementById('pfResults').style.display = 'block';
}