The Rock Meter is found in the lower right corner of the screen (Lower left in Guitar Hero World Tour), and measures how well you're doing while playing a song. It is divided into four colored sections: green, yellow, red and flashing red. At the beginning of each song, the Rock Meter's needle is set to the center (except for encore songs, where it starts at middle green). As you correctly play, or "hit," a note, the needle moves one step to the right (towards the green section). Conversely, as you miss a note or overstrum, the needle moves three steps to the left (towards the red section). If the needle reaches the far left of the meter, the player fails the song. However, if you are in flashing red, just barely hanging in there, you can activate Star Power and for every note you hit, the needle will drastically move to the right (green) giving you that extra boost to help you through a song.
- In Guitar Hero and Guitar Hero 2, the guitarists frown when the rock meter is red. Their facial expressions are blank/neutral when the rock meter is yellow, and show their usual expressions when the meter is green. Since Guitar Hero III, facial expressions never change.
- In all Guitar Hero games, the rock meter measures how the audience feels about your performance: when the rock meter is yellow, the crowd cheers normally; when it's green, their cheers get louder; when it's red, they start booing you.
- In Guitar Hero: Warriors of Rock, Judy Nails has a special ability that alters the rock meter; "Crowd Hyper." With this power, the rock meter starts at the middle of the green, like with encore songs. The rock meter can then go above the green momentarily before gaining a power star and resetting to the top of the green. Once Judy has transformed into her warrior form, her ability is upgraded to "Crowd Hyper +" With this upgrade, the rock meter starts at the maximum.