1. Identify the key of the piano song. The key is usually indicated at the beginning of the sheet music or score.
2. Determine the interval difference between the piano key and the trumpet key. In general, the trumpet is pitched in Bb (B flat), which means it sounds a whole tone lower than the written pitch. So if the piano song is in the key of C, you would need to transpose it up a whole tone to the key of D to match the trumpet's range.
3. Transpose the notes in the piano song by adjusting them according to the interval difference. For example, if you are transposing from the key of C to the key of D, you would raise each note by a whole tone. C becomes D, D becomes E, and so on.
4. Adjust sharps and flats as necessary. When you transpose a song, you may need to add or remove sharps and flats to maintain the correct intervals between notes.
5. Review the transposed song and make sure it sounds correct. Play it on a trumpet or use a transposition tool to verify the accuracy of your transposition.
6. Write the transposed song in the new key. You can rewrite the sheet music or notation to reflect the new key, or you can use notation software that allows for easy transposing.
Remember, transposing can affect the overall musical context, particularly if the song contains certain chords or harmonies. If you are unsure about transposing, you may want to consult a music theory resource or a musician experienced in transposition.