A What?

A4 that's what.

This is the size I use as default for my digital photo albums. I can easily get paper of all weights in this size and it fits into readily available plastic sleeve albums.

The actual size of an A4 page is well worth knowing as you will need this when you set up your page software. The official size for A4 is 210mm x 297mm.

The size is set according to the International Standards Organisation standard known as ISO216 which covers all the A, B and C sizes. You can find a full explanation of these along with some useful tables and some wonderfully interesting looking mathematical formulae, which I will ignore, on Wikipedia .