The internet weighs about as much as a grain of sand

Physicist Russell Seitz calculated that all the electrons in motion storing and transmitting data across the internet at any instant have a combined mass of roughly 50 grams — about the weight of a strawberry. The actual data centres and cables weigh millions of tonnes, but the electrons encoding the information are almost nothing. Information itself is remarkably lightweight.

Source: Seitz, R., 'The Internet weighs about 50 grams', Nature (2012)