A4 Paper
A4 paper is the most popular size of paper in use in the UK today. It fits all standard sized printers, including all the common standard size inkjet and laser printers.
Paper Sizes
The current standard for office paper is ISO 216 of 1975, which defines the paper sizes known as A and B. It is the A series which is of interest to us.
The A series of paper is based on a full size sheet of paper, known as A0. This is one square metre in size, with an aspect ratio of one to the square root of two.
In calculating the various paper sizes, rounding to the nearest millimetre is used.
It is a fairly simple process to get the smaller A sizes from the large standard A0, everything is done by halving the next biggest size.
So, to get two A1 sized sheets of paper from an A0 sheet, you just halve it across the length. So, you start off with A0, which is 841mm by 1189mm. You leave the width the same, and halve the long, 1189mm side, giving you two sheets 594mm by 841mm.
If you can't remember which side to halve, just think what would happen if you halved the wrong side, you would end up with two long narrow sheets of paper, which is clearly not what you would want.
To get A2, you have the A1, and so on to halving A3, which is 297mm by 420mm to get A4, which is 210mm by 297mm.
You will see that the longer side of the next smaller size is always the same as the shorter side of the next larger size, subject to rounding as mentioned.
B series are a different version, based on a different aspect ratio.
Envelope Sizes
It is the C series which is more of interest to us when looking at A sizes, as C series is usually used for envelopes, and is the size required to fit an A sized sheet into it.
So, if you want to put an A4 sheet in an envelope unfolded, you use a C4 envelope. If you fold your A4 sheet in half, it becomes A5, and will fit in a C5 envelope.
Buy A4 Paper
You can buy A4 paper online here