Photo Print Size Guide

Sizes, shapes, and the megapixels each one needs

Photo prints come in a small number of standard sizes. Each has a fixed shape, and that shape is where most printing disappointment comes from.

This chart lists them in inches and centimetres, with the aspect ratio beside each and the minimum megapixels for a sharp print at 300 DPI. Two questions, answered before you spend anything: will it crop, and is the file big enough.

Your camera has a shape and so does the paper

A DSLR or mirrorless camera shoots 3:2. Most phones shoot 4:3. Print sizes have their own ratios, and where the two disagree, something gets cut off.

The cut is not random and it is not gentle. A 3:2 photo printed at 10×8 loses a strip from each end, and if you composed tightly, that strip has somebody's ear in it. Matching the shape first is the whole trick, and where you cannot match it, crop the image yourself so you decide what goes rather than letting a lab's automatic centre-crop decide for you.

The ratio families

• 3:2. 6×4, 9×6, 12×8 inches. Straight off a DSLR sensor with nothing lost.
• 5:4. 10×8 and 20×16. Noticeably squarer, and a 3:2 original gives up a strip to get here.
• 7:5. 7×5 and 14×10, sitting between the other two, so the crop from 3:2 is small.
• 4:3. Phone photos and compact cameras. The A-series is near this at about 1.41:1, which is close enough to look right and far enough to need checking.
• 1:1. Square, which crops every rectangular original there has ever been.

Metric and imperial never quite line up

Photo sizes are imperial by convention almost everywhere, including in countries that use nothing else metric, and the near-matches that produces cause real problems.

A 6×4 inch print is 152 × 102 mm. A5 is 148 × 210 mm. Similar in one dimension, wildly different in the other, so a 6×4 print does not sit properly in an A5 frame or sleeve however much the numbers look like they should agree.

The metric equivalents you see quoted, 10×15 cm and 13×18 cm, are close to 6×4 and 7×5 without being identical. A frame bought for one will show a white edge around the other, or clip it. Check the actual millimetres on a frame, on a mount, on an album, rather than trusting that a name matches, because a few millimetres is the whole difference.

What the frame hides

A frame covers the outer edge of the print under its rebate, usually three to five millimetres all round. Anything important that close to the edge is gone.

A mount hides considerably more, and its aperture is deliberately cut a few millimetres smaller than the print so the print cannot slide through it. Standard apertures assume standard print sizes, which is one more argument for printing to a named size rather than a custom one.

So leave breathing room around the subject instead of composing to the exact edge. And if a print has a specific frame waiting for it, measure the aperture before ordering: frames sold as 10×8 sometimes mean the outside of the frame rather than the image area, and that is a costly assumption to discover at home.

Finish, and how long any of it lasts

• Gloss. The strongest colour and the deepest contrast, and it shows every fingerprint. Behind glass it is a mirror.
• Matte. No reflections at all, slightly flatter colour, and much the better choice for framed work or for anything that will be handled.
• Satin or lustre. The compromise most labs default to, and usually the right answer if you are not sure.

Prints fade with light, and how quickly depends on the ink, the paper and where it hangs. Direct sunlight is the thing that kills them; pigment inks last considerably longer than dye inks. For anything you care about, the real archive is the digital file, which does not fade and costs nothing to reprint.

Using the chart

1. Work out your photo's aspect ratio. If you are not sure, the aspect ratio calculator on this site will tell you.
2. Pick a print size whose ratio matches, or comes close.
3. Check the megapixel figure. Under it and the print will look soft, however good the photo is.
4. Preview the crop before ordering. The minimum-megapixel numbers assume 300 DPI, and a poster seen from across a room is perfectly fine below that.