PictureBorderAdd a border

Printing a bordered photo

On screen a border is a share of the picture. On paper it is millimetres. This guide is the arithmetic between the two, as the studio does it.

Millimetres become pixels at a resolution

A file has pixels, not millimetres. It only gets a physical size when something prints it at a resolution: so many dots per inch. The studio asks for that number when you choose mm or in as the width unit, and converts with one rule — millimetres ÷ 25.4 × DPI, rounded to a whole pixel. 300 DPI is the usual figure for a photo lab print, and the one every print size on this site assumes.

3 mm
35 px at 300 DPI · 24 px at 200 DPI
5 mm
59 px at 300 DPI · 39 px at 200 DPI
10 mm
118 px at 300 DPI · 79 px at 200 DPI
20 mm
236 px at 300 DPI · 157 px at 200 DPI
40 mm
472 px at 300 DPI · 315 px at 200 DPI

The readout under the width field prints the same conversion while you type, for example 472 px = 40.0 mm at 300 DPI. Change the DPI and the pixel figure changes; the millimetres you typed stay what you typed.

What a print size needs

The Fit menu's print sizes are the same arithmetic in reverse: the paper's size in inches or millimetres times 300. The whole photo is placed on that canvas, never cropped, and the border fills what is left; the frame's own width is the narrowest border it will allow.

4 × 6 in print
1200 × 1800 px at 300 DPI, turned to landscape for a landscape photo
5 × 7 in print
1500 × 2100 px at 300 DPI, turned to landscape for a landscape photo
A4 print
2480 × 3508 px at 300 DPI, turned to landscape for a landscape photo

A photo with fewer pixels than the print size is scaled up to fill it, and a lab will print it softer than a photo that had the pixels to begin with. The border itself is drawn at the output size, so it stays sharp either way.

Home printers and their margins

Many home printers cannot put ink right to the edge of the paper and leave a thin unprinted strip, or enlarge the picture slightly to print borderless and lose a little at each edge. A deliberate border helps in both cases: a few millimetres of white at the edge survives either treatment better than a photo that runs to the edge. Check your printer's own settings for borderless printing and scaling; set the print size to 100% so the millimetres you set are the millimetres you get.

Why a mat’s bottom is wider

Framers usually cut a mat a little deeper at the bottom than at the top and sides. A picture placed in the exact middle tends to look as if it has slipped down; a slightly heavier bottom lifts it to where the eye expects the centre to be. The photo mat page starts at 1.15 times the side width and lets you set it, and the same Bottom weight control appears on the wedding and occasion frames, where the extra depth also gives a caption room.

A 40 mm mat at 300 DPI with a weighted bottom, on a 6 × 4 in photo — drawn by this site's renderer: a 1800 × 1200 picture becomes 2744 × 2380.

What this guide cannot tell you

  • How a particular lab or printer will treat the file. Labs differ in how they crop to paper sizes; ask for “no cropping” or “fit to paper” where it is offered.
  • Colour on paper. Screens and printers show colour differently, and this site does no colour management for print.

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