Picture Mounts Measuring Guide
How to Measure for a Custom Picture Mount
Measuring accurately is essential when ordering a custom picture mount to ensure a perfect fit for your existing frame. Use this easy guide to get your measurements right and create a professional-looking framed piece.
Should I Measure the Internal Frame or the Glass?
For the most accurate fit, always measure the glass size or hardboard inside your frame—not just the frame’s internal dimensions. The mount needs to fit behind the flexible tabs or clips that hold the glass and artwork in place.
Measuring the glass or backing board gives you the exact external mount size needed, ensuring your custom mount fits securely within your frame.
If you don't have a frame and require just the mount it is up to you to decide the outside dimensions of your mount.
How Do I Measure the External Mount Size?
- Carefully remove the glass or backing board from your frame.
- Measure the width and height of the glass or backing in millimetres (or inches).
- Use these measurements as your external mount size when ordering.
Tip: Double-check measurements before submitting your order to avoid any fit issues.
What Should the Aperture (Inside Window) Size Be?
How to measure your artwork for a picture mount
How to measure your artwork when it has a border
The aperture size is the visible window cut into your mount to showcase your artwork or photo.
We cut your mount exactly to the aperture size you specify, so it should be slightly smaller than your image to prevent it falling through the aperture.
- Measure your image’s width and height in millimetres.
- Subtract 6mm from both measurements to allow a 3mm overlap on each side.
Example: For an image measuring 350mm x 270mm, the aperture should be 344mm x 264mm as shown below.
For larger prints, subtract 10mm for a wider 5mm overlap, which helps keep rolled or flexible prints flat and securely in place.
If your image has a white border and you'd like a portion of it (e.g. 5mm) to show before the mount begins, simply measure the exact size of the image and increase that size by 10mm each way.
For example, if your image area (not including the white border) measures 400mm x 300mm, and you want 5mm of the white border to show all the way around, you would add 10mm to both dimensions — resulting in an aperture size of 410mm x 310mm.
You can then set the external mount size to fit your frame. If you're not using a frame, you're free to choose any border width you like for the outer dimensions.
If you want the entire border of your print to remain visible within the mount, measure the full size of the print including the border, then subtract 6mm from both the width and height.
This slight reduction allows for a 3mm overlap on each edge, ensuring the print stays securely in place behind the mount.
For example, if your print (including border) measures 500mm x 400mm, you would enter the aperture size as 494mm x 394mm.
How Do I Choose the Border Width?
The border width (the mount’s visible frame) affects the aesthetics of your framed artwork.
- Standard border widths range from 30mm to 60mm.
- Wider borders can balance larger frames or create a gallery-style look.
- Borders can be evenly sized or bottom-weighted, depending on your style preference.
What About Double Mounts and Acid-Free Backing?
Adding a double mount or an acid-free backing board provides extra depth and protection.
- These layers add thickness, so ensure your frame can accommodate the added depth.
- Acid-free backing protects artwork from acid damage, increasing longevity and preservation.
Can I Design My Mount Online?
Yes! Our online custom mount designer lets you:
- Enter exact external and aperture sizes
- Choose from a wide range of mount colours
- Select single or double mounts
- Add optional acid-free backing for extra artwork protection
Final Tip: Measure Your Glass for the Best Fit
Always measure the glass size for the most reliable mount fit. This ensures your custom picture mount fits neatly under the tabs and holds your artwork securely.
If you're looking for custom picture frames, canvas floating frames, or would like your photos printed and professionally framed, please visit our main website — The Picture Gallery — where you'll find our full range of framing services and products.