Spotify and Pandora both require a minimum bandwidth of between 150 and 160 kilobits per second for streaming over the web. This is equivalent to 72 megabytes of data usage per hour.
Internet radio bandwidth use depends on the quality of the data stream, measured in kilobits per second. Pandora's 300 kbps "high quality" setting uses double the amount of data as the standard quality stream. Internet radio services often use a reduced quality stream for mobile applications. Spotify's normal quality stream for mobile devices is 96 kbps.
The quality of streaming audio is determined by the amount of compression that has been applied to the original file. More compression reduces the quality of the audio as it reduces the amount of bandwidth needed to transmit.