How do you transpose piano key to cello key?

To transpose from piano to cello, you need to account for the cello's tuning, which is a fifth lower than the piano. For example, if the piano part is in C major, you would transpose it down a perfect fifth to G major for the cello. This means you would lower each note on the piano by a fifth or, alternatively, move each note up to the corresponding note in the cello's range. Always check the key signature and adjust accordingly to ensure the music fits within the cello's capabilities.