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Choosing the right picture frame should be simple, but size labels on product pages often make it confusing. Customers regularly mix up the size a photo frame holds (the artwork size) with the picture frame’s outer dimensions. Some of them are unsure what an aperture or mount size actually means. That leads to wrong orders, last-minute returns, and time wasting.
Product listings don’t always spell this out. Seeing “A0 picture frame” might make you think the whole frame measures A0. In fact, it means the photo frame is made to hold an A0 artwork.
The same rule applies to mounts, Perspex/acrylic glazing and backing boards. I mean, the listed size is the size they’re made to fit, not the final visible or outer measurement.
This guide clears up those common mix-ups. You’ll learn how picture frame sizes, aperture sizes, and accessory sizes relate to each other. How small manufacturing tolerances work, and how to read our made-to-measure tool so you get the exact fit you need.
Before diving into the details, it helps to clarify a straightforward point. The size written on any picture frame refers to the artwork it is designed to hold. Everything else, including the photo frame’s outer measurements, is secondary.
Once you understand this, the entire sizing system at Alison Kingsgate becomes much easier to read.
When a picture frame is listed as A0, A3, 9x7", or 16x16" picture frame, that size represents the artwork size the picture frame is designed to hold. It does not reflect the full outer measurements of the photo frame, nor does it represent the visible opening at the front.
Each frame has three different measurements involved:
The outer size changes depending on the style you choose. Some picture frames have slim mouldings, such as sleek picture frames, while others have wider, more decorative mouldings. It naturally adds extra centimetres around the outside. That's why two frame styles listed as 16x16" can look noticeably different in overall size when placed side by side.
Inside every picture frame is a small ledge called the rebate. This is the place where your artwork, mount, acrylic, and backing board sit securely once assembled.
The rebate keeps everything in place and is slightly smaller than the artwork area on the front. That's why your art slips neatly behind the edge of the photo frame.
To ensure a comfortable fit, manufacturers allow a small tolerance in the rebate, typically a few millimetres. It helps prevent the artwork from feeling too tight or difficult to insert. Furthermore, it ensures the pieces can sit square and safely, no matter the material you're framing.
Many customers assume a 16x16" picture frame has an outer size of exactly 16x16". That's never the case. The outer size is always larger because the moulding adds extra width on all sides.
A slim photo frame style might add only a small amount, while a deep or bold moulding can increase the outer size by several centimetres. Since each frame style has its own proportions, the outer dimensions vary even when the artwork size remains the same.
That's why the outer size shouldn't be used for wall planning or gallery layouts. Instead, focus on your artwork size first, the listed frame size, and choose the photo frame design you like. The final physical size will be determined by the moulding you've selected.
Picture mounts are one of the most common sources of confusion, mainly because they involve two separate measurements. Those measurements are the mount size and the aperture size.
Once you understand what each one represents, choosing the correct mount becomes a simple step-by-step process.
The picture mount size indicates which photo frame the mount fits.
If a mount is listed as A1, it means it is designed to fit inside an A1 picture frame. The outer edges of the mount match the inner space of the picture frame, so the two pieces fit perfectly together.
For example:
The mount size never matches the artwork's size. It only reflects the frame size it is designed to sit inside.
The aperture size is the cut-out in the middle of the mount, and this area represents the artwork size.
For example, a mount listed as A1 with an A2 aperture means:
Think of the aperture as the “window” that showcases your artwork, while the mount size acts as the outer border that fits the photo frame.
Apertures are always cut a few millimetres smaller than the artwork size. It is an intentional rule because it helps keep your artwork from slipping through the opening.
This minor adjustment, known as a slight undersize, holds the artwork firmly in place without covering too much of the picture. Manufacturers usually reduce each side by a few millimetres, just enough to create a secure hold while still keeping the piece neatly centred.
When selecting a picture mount, start with the artwork size. Match your art to the correct aperture size, then choose the picture frame size for the mount to fit inside.
If you prefer a tight, clean look, go for a narrower border around the aperture. If you want your artwork to stand out more, opt for a wider border, which adds space and creates a more balanced presentation.
Picture Mounts can be kept simple with a single aperture at the centre, or designed with more creative layouts. But for most art and photography, a single aperture paired with the correct border width gives a clear, polished result.
The creative layout of picture mounts is used for multi-aperture picture frames. It is the mount that converts a simple photo frame into a multi-photo frame.
Alongside picture frames and mounts, framing accessories like acrylic glazing and backing boards follow the same easy-to-understand sizing system. Once you know how these pieces are measured, replacing or upgrading parts of your frame becomes straightforward.
Let's discuss the size system for framing accessories step by step.
Acrylic glazing (also known as Perspex) is always listed by the frame size that it fits.
If the product says A0 acrylic sheet, it means the sheet is cut to fit any A0 picture frame. It keeps things simple. You don't need to match glazing to your artwork or calculate extra allowances. Just select the size that corresponds to your frame. Let's see examples:
No matter which picture frame style or moulding you choose, the acrylic is designed to sit neatly within the frame's internal structure.
Backing boards follow the same rule. The size refers to the photo frame they are made for, not the art or the outer measurements.
Let's see examples:
Because backing boards sit directly behind your artwork or mount, their size must align perfectly with the frame's internal space.
Acrylic sheets and backing boards sit inside the photo frame behind the rebate. So, they must match the frame’s internal size with precision. If they’re even slightly off, the fit won’t be secure, and the layers inside the picture frame can shift or bend.
That is why all accessories, mounts, glazing and backings follow a single unified sizing system. By matching each item to the frame size, everything layers together correctly, stays firmly in place, and protects your artwork as intended.
It also means you can confidently replace parts in the future without having to re-measure your artwork or frame.
Custom sizes are often the best choice for artwork that falls outside standard measurements. At Alison Kingsgate, we offer custom framing services. For this purpose, we have a dedicated page that gives you complete flexibility to order a custom-sized photo frame.
We have a properly made-to-measure tool that allows you to order bespoke dimensions for your artwork. Our made-to-measure tool keeps the process simple by using the artwork size as the central reference point.
When you enter your dimensions into the made to measure picture frames tool, those numbers represent the artwork size the frame will hold. So if you type in 40x43cm, the picture frame you receive will be designed to fit a 40x43cm art piece.
There’s no need to add extra space or calculate tolerances yourself. The system does all of that in the background. You only enter the exact size of your artwork, and our team will build your photo frame around those measurements.
If you choose to include a picture mount, the sizing becomes just as straightforward. The frame size follows the outer mount size, and the aperture represents the artwork size, for example:
If your custom frame is 62x68cm and you choose a mount with a 40x50cm aperture, the mount will sit inside the frame and display a 40x50cm artwork.
So, again, the aperture size you enter should match the exact size of your artwork. In our made-to-measure tool, we only allow you to enter the aperture size of the mount, since the mount size is already set to framesize.
Custom acrylic glazing and backing boards follow the same simple logic as the frame. Their size is based on the frame size, not the artwork size.
That means:
Once you choose your custom frame dimensions, all accessories automatically align. It gives you a complete and accurate fit without extra steps or calculations.
Getting accurate measurements from the start helps you choose the right picture frame or mount without guesswork. Different types of artwork need slightly different measuring approaches, so it's worth taking a moment to measure yours carefully.
Let's deeply dive into it!
For posters, fine art prints and similar pieces, measure the full visible height and width of the sheet. Make sure the artwork is lying flat, and use a firm ruler or tape measure so the edges don’t curl while measuring.
Some prints come with narrow white borders. Decide whether you want those borders visible inside the frame or hidden behind a mount. If you plan to hide them, measure only the printed artwork area. If you want the borders included, measure the full sheet size.
In simple words, do measurements of your art piece according to the area that you want to display.
Photographs and some art prints often include built-in borders that surround the image. Before ordering a picture frame or mount aperture, check whether the border is part of the design or simply extra space you plan to trim later.
If you want the full sheet displayed, use the complete measurement. If you intend to show only the image area, measure the printed section alone and pair it with a picture mount aperture that matches this inner measurement.
Handmade pieces, sketches and craft projects sometimes have uneven edges. In these cases, measure the tallest and widest points of the artwork, even if those edges are not perfectly straight.
For pieces with soft or uneven borders, it often helps to place a mount over the artwork. A mount can hide irregular edges, keep the art centred, and give you a clean finished look inside the picture frame. If you choose this route, base your aperture setting on the area you want most visible.
Take a few extra moments to measure correctly. Ensure the picture frame fits beautifully and your artwork sits neatly inside without gaps or pressure points.
Once you know how picture frame sizing works, the next step is choosing the right size for your wall. Many customers start by measuring the space where the picture frame will hang.
Unfortunately, this can lead to confusion because the outer size of a photo frame is never fixed. A better approach is to work from the artwork size first and let the frame style follow.
Two picture frames listed as the same size can look completely different once hung on the wall. It is because each photo frame style has its own moulding width and depth.
A slim frame adds only a small amount around the artwork, while a bold or deeper moulding adds much more. It changes the overall outer measurement.
If you plan your layout using outer sizes, you may end up with gaps between picture frames or a gallery wall that doesn’t line up as you expected. Since outer dimensions vary by style, they’re not a reliable reference point for designing a layout.
A more accurate method is to plan using your artwork size, not the outer frame size. You should start with the size of the piece you want to display. Choose the picture frame size that matches it, then pick a picture frame style that suits your preferred look.
This approach works for both standard and made-to-measure picture frames. It keeps your planning simple, avoids surprises, and ensures each piece sits comfortably in your chosen layout.
When creating a gallery wall, consistency is the key to a clean, organised look. The easiest way to achieve this is to choose a set of artwork sizes and stick to those measurements throughout the layout.
You can mix A-sizes and inch sizes if needed, but make sure each group is intentional. For example, pairing A4 prints with 8x10" photos works well if you balance them across the arrangement.
By planning with artwork sizes rather than outer photo frame measurements, you'll create a layout that stays aligned no matter which picture frame styles you choose.
This approach gives you the freedom to mix colours, photo frame types and mount options without losing visual balance on the wall. Try this, you're going to love it.
To make choosing the right picture frame easier, Alison Kingsgate offers a wide range of standard sizes across A-sizes, metric formats and traditional inch measurements. These cover most photography, prints, posters and modern décor needs.
If your artwork falls outside these options, you can use our made-to-measure service for a perfect fit. It will fulfil your custom size requirement.
A-sizes are widely used for posters, design prints and general artwork. They’re part of an international sizing system, so they’re helpful when framing anything printed to standard paper sizes, whether it’s an A4 document, an A3 art print or a large A0 poster.
Each size links directly to a matching picture frame size. It makes A-sizes easy to work with when you want a clean, consistent display across your home or workspace.
Metric sizes are widely used for prints, posters, and home décor pieces produced across Europe. These dimensions cover a broad range of square and rectangular formats. It makes them suitable for both modern artwork and everyday wall prints.
If you’re framing contemporary posters, family photos from phone prints, or artwork purchased from European makers, cm sizes provide a straightforward fit without needing adjustments.
With options ranging from compact 15x15 cm picture frames to large 100x90 cm displays, the metric category offers plenty of flexibility for statement pieces, gallery walls, or balanced sets across a room.
Inch-based sizes are very common for photographs, portraits, and studio prints. Formats like 6x4", 7x5", 8x6", 16x16", and many others are often used by photographers and come as standard sizes in photo labs.
These measurements also work well for art pieces created on canvas paper or prints ordered from online stores. They follow traditional photography proportions.
Alison Kingsgate offers a wide range of these sizes, from small tabletop frames to large wall pieces.
Custom sizing is ideal when your artwork doesn’t match any standard picture frame measurements. It includes posters with unusual proportions, handmade artwork with uneven borders, panoramic prints, or pieces that have extra white space you want to show.
If your measurement doesn’t appear in our standard A-sizes, metric sizes, or inch sizes, the made-to-measure option lets you enter the artwork size directly. With it, you can create a photo frame that complements your artwork perfectly.
Using custom sizing ensures your artwork gets a precise, tailored fit without compromising on its original shape or presentation.
While ordering a picture frame, customers often make mistakes about size and other details. Let's discuss the most common mistakes that buyers make and how to avoid them.
Mistake 1: Assuming frame size equals the outer size
Many people think the listed photo frame size refers to the outside edges. In reality, frame size always refers to the artwork it holds.
The fix: Plan your order using your artwork size, and let the picture frame style determine the final outer measurement.
Mistake 2: Ordering the wrong aperture for picture mounts
Some users enter the frame size rather than the artwork size, resulting in an incorrect mount opening.
The fix: For custom mounts, the aperture should always match the exact artwork size you’re framing.
Mistake 3: Ordering acrylic based on artwork size instead of frame size
A standard error is selecting glazing that matches the print rather than the whole frame.
The fix: Acrylic always follows the frame size, not the artwork size.
Mistake 4: Measuring artwork inaccurately
Tight measurements, rounded numbers, or guessing can cause prints not to fit.
The fix: Measure the visible height and width carefully, and note whether there are borders or uneven edges.
Mistake 5: Using outer size to plan gallery walls
Outer sizes vary by photo frame style. It leads to gaps or misaligned layouts.
The fix: Plan gallery walls using artwork sizes so the arrangement stays consistent across different picture frame designs.
By avoiding these mistakes, you can order the perfect frame for your artwork.
A clear overview of what each size label represents across picture frames, mounts, glazing, and backing. This table helps users understand exactly what they’re selecting.
| Product Type | Listed Size Means | Use It For |
| Picture Frames | The artwork size is the size of the picture frame it is built to hold. | Choosing the right picture frame for prints, posters, photos, and artwork. |
| Picture Mounts | The outer size matches the photo frame. The aperture matches the artwork size. | Adding a border, creating spacing, or highlighting the artwork. |
| Acrylic / Perspex Glazing | Cut to the same size as the frame it fits into. | Replacing glazing or upgrading to clearer, safer acrylic. |
| Backing Boards | Cut to match the picture frame size for a secure fit. | Strengthening the photo frame, keeping artwork flat, or replacing damaged backboards. |
| Custom Picture Frames | Built precisely to the artwork size entered. | Irregular art, unique posters, panoramic prints, and handmade pieces. |
| Custom Picture Mounts | Picture Frame size = outer mount size; aperture = artwork size. | Controlling visible space or adapting artwork to a larger photo frame. |
| Custom Acrylic & Backing | Cut to the custom frame size. | Ensuring the complete custom frame package fits together correctly. |
Choosing the right picture frame size becomes much easier once you understand what each measurement refers to. Photo Frames are listed by the artwork size they hold, mounts list both their outer and aperture sizes, and accessories follow the same simple system.
At Alison Kingsgate, every picture frame, mount, acrylic sheet, and backing board follows one consistent sizing method. It removes guesswork and ensures each component fits together precisely as it should.
You can explore a wide range of A-sizes, metric sizes, and inch sizes on the site. You can use the made-to-measure tool when your artwork has unique proportions. Either way, you’ll be able to create a frame that matches your artwork accurately and looks right in your space.