Free Picture Frame Calculator

What This Frame Size Calculator Does

Choosing the right dimensions for a picture frame can be challenging when you want a custom look. A dedicated frame size calculator eliminates guesswork by computing both inner and outer frame dimensions, the required mat size, and the total molding length needed. Whether you are mounting a family photo, a piece of art, or a digital print, this tool acts as a complete custom frame dimensions estimator and mat size calculator for any DIY picture frame project.

The calculator accepts three primary inputs: the picture’s width and height, the desired border (molding) width, and optional mat dimensions. Based on these values it returns the external frame height and width, the internal viewing area, and the perimeter of the frame – information that directly guides your material purchases and cutting plan.

Key Measurements Explained

• Picture size – the actual dimensions of the artwork or photograph you want to frame.
• Border width – the width of the frame molding (the visible strip that surrounds the mat and picture).
• Mat size – the extra space (usually white or colored board) placed between the picture and the frame. The calculator lets you set separate mat heights for top/bottom and left/right if needed.
• Rabbet width – the recess in the frame where the picture and mat sit; it slightly reduces the visible mat area. A typical rabbet value is around 1/4 inch.
• Fudge factor – a small allowance (commonly 0.05 inches) added to account for minor cutting or assembly errors.

How to Use the Calculator

1. Choose your units (inches, centimeters, etc.) and enter the border width (molding thickness) in the appropriate field.
2. Input the height and width of your picture – for example, 12 by 12 inches.
3. If you want a mat, specify the mat height and mat width (the amount of blank space visible around the picture). Otherwise leave these as zero.
4. The calculator instantly shows the outer frame dimensions and the inner (viewing) dimensions, along with the total molding length (the perimeter of the frame).
5. For fine adjustments, expand the Frame adjustments section to set the rabbet width and fudge factor. The output values update automatically.

The molding length is calculated assuming 45° miter cuts at the four corners. Actual length may vary slightly depending on joint type and miter accuracy.

Formulas Behind the Calculations

All frame dimensions are derived from the picture size, mat size, border width, and rabbet width.

Outer Frame Dimensions

$$F_{\text{height}} = P_{\text{height}} + (M_{\text{height}} + B) \times 2$$ $$F_{\text{width}} = P_{\text{width}} + (M_{\text{width}} + B) \times 2$$

Inner (Viewing) Dimensions

$$I_{\text{height}} = P_{\text{height}} + (M_{\text{height}} - R) \times 2$$ $$I_{\text{width}} = P_{\text{width}} + (M_{\text{width}} - R) \times 2$$

Molding Length (Perimeter)

$$F_{\text{perimeter}} = (F_{\text{height}} + F_{\text{width}}) \times 2$$

Where:

• $F_{\text{height}}, F_{\text{width}}$ = outer height and width of the frame
• $I_{\text{height}}, I_{\text{width}}$ = inner height and width (the visible opening)
• $P_{\text{height}}, P_{\text{width}}$ = height and width of the picture
• $M_{\text{height}}, M_{\text{width}}$ = mat height and width (if no mat, use 0)
• $B$ = border (molding) width
• $R$ = rabbet width

If you need different top/bottom mat heights, replace $M_{\text{height}}$ with $\frac{M_{\text{top}} + M_{\text{bottom}}}{2}$. Similarly, for left/right differences use $\frac{M_{\text{left}} + M_{\text{right}}}{2}$.

Practical Examples

Example 1 – Simple Frame without Mat
You have a 4 × 6‑inch picture and want a 1‑inch border. No mat is used.

$$F_{\text{height}} = 4 + (0+1)\times2 = 6\ \text{in}$$ $$F_{\text{width}} = 6 + (0+1)\times2 = 8\ \text{in}$$ $$F_{\text{perimeter}} = (6+8)\times2 = 28\ \text{in}$$

The frame’s outer size is 6 × 8 inches, and you need 28 inches of molding.

Example 2 – Finding the Mat Size from a Known Frame
You have a ready‑made frame that is 16 × 20 inches with a 1‑inch border and a 0.25‑inch rabbet. The picture is 8 × 11 inches. Determine the visible mat size.

First, find the inner frame dimensions:

$$I_{\text{height}} = 16 - 1\times2 = 14\ \text{in}$$ $$I_{\text{width}} = 20 - 1\times2 = 18\ \text{in}$$

Now rearrange the inner dimension formula to solve for mat size:

$$M_{\text{height}} = \frac{I_{\text{height}} - P_{\text{height}}}{2} + R = \frac{14-8}{2} + 0.25 = 3.25\ \text{in}$$ $$M_{\text{width}} = \frac{I_{\text{width}} - P_{\text{width}}}{2} + R = \frac{18-11}{2} + 0.25 = 3.75\ \text{in}$$

The visible mat will be 3.25 inches on the top/bottom and 3.75 inches on the sides.

Collage Mode

For projects that contain multiple pictures, the calculator has a dedicated collage mode. You can enter up to five picture sizes, and the tool will help you design a layout that fits within a single frame. Once you’ve settled on a collage arrangement, switch back to picture mode to obtain individual framing details for each opening.

Standard Picture Frame Sizes

The following table lists common frame dimensions by orientation. All values are height × width in inches.

Category	Popular Sizes
Portrait	7 × 5, 10 × 8, 11 × 8.5, 14 × 11, 20 × 16
Wall / General	8 × 10, 10 × 12, 12 × 15, 16 × 20, 20 × 24
Table / Desk	4 × 6, 5 × 7, 6 × 8, 5 × 10, 8 × 8
Landscape	16 × 16, 20 × 16, 18 × 24, 24 × 24, 24 × 36, 20 × 40

These standards can serve as a starting point, but the calculator accepts any custom dimensions you need.

Why Use a Dedicated Frame Size Estimator

Manually measuring and calculating frame dimensions leaves room for error, especially when mats and rabbets are involved. A purpose‑built picture frame size calculator ensures consistent results, saves material waste, and helps you achieve a clean, professional finish on every DIY picture frame project. By entering just a few numbers you receive immediate outer and inner sizes, mat allowances, and molding length – everything needed to cut and assemble your frame with confidence.