Learn the basics of music theory
Playing piano by ear requires a basic understanding of music theory. Start by learning the basics of scales, chords, and intervals. This will help you identify and distinguish different notes and chords when listening to songs. Familiarize yourself with the different modes, scales and chord progressions used in popular music.
Listen actively
Play songs you like on repeat and listen actively. Identify the melody, harmony, and rhythm. Focus on the chords and patterns of the song. This can be easier if you already have a basic understanding of music theory.
Play along with recordings
Start by playing along with recordings of your favorite songs. It may take some time to figure out the correct notes and chords, but with practice, you will start to recognize the patterns and develop your ear. You can also slow down the recordings to play at a more manageable pace using software such as Audacity.
Experiment with different chord progressions
As you become more comfortable playing along with songs, try experimenting with different chord progressions. Start by playing simple songs with only a few chords then move on to more complex songs with more chords. There are many resources available online for chord progressions and song charts such as Ultimate Guitar.
Practice regularly
Practicing regularly is key to developing your ear and becoming better at playing piano by ear. Set aside time each day to practice and focus on developing your listening skills. With dedication and practice, you will be able to play your favorite songs by ear and even start improvising your own music.