Mount Size Guide
How to choose the right picture mount — border width, aperture and single vs double — so your artwork sits perfectly inside the frame.
How big should a mount be? A mount has two measurements: the aperture (the window your picture shows through) and the border (the card around it). As a rule of thumb, a border of 40–70 mm suits most pictures — wider borders look more gallery-like. The aperture is cut a few millimetres smaller than your artwork so the edges are held neatly behind the card.
The three measurements that matter
| Measurement | What it is |
|---|---|
| Artwork size | The picture you’re framing |
| Aperture (window) | Cut ~3–5 mm smaller than the artwork per side, so the edges sit behind the mount |
| Border | The visible card around the aperture — this sets the overall mount (and frame) size |
Choosing your border width
Border width is about taste and balance:
- 40–50 mm — a neat, classic border for photos and prints.
- 50–70 mm — a more generous, gallery-style border that gives the picture room to breathe.
- 70 mm+ — a statement border for art prints and feature pieces.
Bottom-weighting: framers often make the bottom border slightly larger than the top and sides — it counters an optical illusion that makes equal borders look bottom-heavy, and gives a balanced, professional finish.
Single or double mount?
| Mount | Best for |
|---|---|
| Single | A clean, classic border — the most popular choice |
| Double | Adds a thin inner border in a second colour for depth and a premium feel |
A worked example
Framing an A4 print (21 × 29.7 cm) with a 50 mm border? The mount — and so the frame opening — would be roughly 31 × 39.7 cm, with the aperture cut a few millimetres inside the print so nothing slips through. You don’t need to do the maths: choose your border and we cut it for you.
Design your mount
Pick your mount colour, border width and single or double mount in our frame builder — or browse frames with mounts to get started. Mounts are cut to order in the UK.
Mount size FAQs
How wide should a mount border be?
Most pictures suit a 40–70 mm border. Narrower looks neat and classic; wider looks more gallery-like. Choose what fits your picture and the wall space.
How is the mount aperture size worked out?
The aperture (window) is cut about 3–5 mm smaller than your artwork on each side, so the edges are held neatly behind the mount rather than slipping through.
Why is the bottom border sometimes bigger?
It’s called bottom-weighting. Equal borders can look bottom-heavy to the eye, so a slightly larger bottom border gives a balanced, professional finish.
What is the difference between a single and double mount?
A single mount has one border; a double mount adds a thin inner border in a contrasting colour for extra depth. Both are chosen when you design your frame.
Related: Frame Size Guide · How to Measure · Frames with Mounts · Design a custom frame
Cut to order in the UKBy our own framers
Single & double mountsYour colour & border
Conservation optionsAcid-free board available
Carefully packagedProtected for delivery