Picture frame sizes use three systems: A-sizes (A4, A3, A2), imperial inches (6x4, 10x8) and metric millimetres. It looks confusing, but it is simpler than it seems, because everything starts with the size of the artwork or photo itself. The frame, mount and final proportions are then built around that. 

Photo prints are usually measured in inches, posters and art prints in A-sizes, and custom framing in millimetres for precision.

By convention, photography and art sizes are quoted width first, then height, which is often the opposite of how measurements are given elsewhere. With photos this rarely matters, since you can flip-reverse the print to the orientation you prefer.

A-sizes explained

We’re used to A-sizes nowadays because that’s what our printers use, and they’re the standard paper sizes used across the UK and Europe. They are also increasingly the standard for posters and art prints. Each size up doubles in area: A4 is twice A5, A3 is twice A4, and so on.

Common photo sizes explained

Because we love to mix metric and imperial to keep ourselves guessing, traditional UK photo print sizes are measured in inches. The classic is 6x4 inches, the size most of us (well, Millennials and older at least…) remember from our days collecting our envelopes of photos from Boots. Because they are smaller, these sizes also suit lower-quality or low-light photos, where going larger would risk making the image look blurry.

How custom frame sizes work

Custom framing starts with the exact size of your artwork. From there the frame is built to fit it precisely, the mount overlap is calculated automatically, and the final external dimensions are adjusted in proportion. You do not need to calculate the finished frame size yourself. You only need the size of the artwork, or if you are having something printed, the size you would like it printed at, and we handle the rest.

How size affects the price

Pricing is structured around these standard sizes. Each size sits in a band with a single, transparent price. So if you’re framing an A3 sized piece, for example, you will have one clear price whichever frame style you choose within that band. This means you can see exactly what your frame will cost as soon as you know your size, with none of the uncertainty traditional framing has often carried. If you already know your artwork is A4 or A2, you already know your price band.

What is DPI, and why does it matter?

DPI stands for “dots per inch”, and it describes image quality at a given print size. Higher DPI means sharper printing and better detail. As a rough guide, 100 DPI is the acceptable minimum and 200 or above is ideal for high-quality prints. Lower-resolution images can look blurry if printed too large. But don’t worry too much about it - our system automatically checks image quality at your chosen size and warns you if the resolution may be too low.

Common mistakes to avoid

Three mistakes come up repeatedly. The first is measuring the existing frame instead of the artwork or object; always start with the piece itself. The second is mixing inches and millimetres, since photo sizes are often in inches while framing is measured in millimetres. The third is printing a low-resolution image too large, which makes any blur or compression more visible. Start with the size of the artwork, and everything else follows from there.