E-readers get heavier with each book

E-readers are meant to let bookworms carry their entire libraries with them without any additional weight – but the devices actually get heavier every time a new text is downloaded.

By Nick Collins, Science Correspondent

30 Oct 2011

The weight difference is unlikely to make much difference to holidaymakers' baggage allowances, however, because each new tome is about as heavy as a single molecule of DNA.

Filling a 4GB Kindle to its storage limit would increase its weight by a billionth of a billionth of a gram

Prof John Kubiatowicz a computer scientist at the University of California, Berkeley, explained in the New York Times last week that storing new data involves holding electrons in a fixed place in the device's memory.

Although the electrons were already present, keeping them still rather than allowing them to float around takes up extra energy – about a billionth of a microjoule per bit of data.

Using Einstein's E=mc² formula, which states that energy and mass are directly related, Prof Kubiatowicz calculated that filling a 4GB Kindle to its storage limit would increase its weight by a billionth of a billionth of a gram, or 0.000000000000000001g.

This is roughly equivalent to the weight of a small virus, while the equivalent number of books – about 3,500 – would weigh approximately two tons.