Ledger lines and middle C

Middle C sits on one short extra line, below the treble staff or above the bass staff, and both mean the same key.

Short lines that extend the staff

Five lines cover only nine positions, from the bottom line to the top line. Music often goes further. When a note is too high or too low for the staff, the writer adds short lines called ledger lines just long enough for that note. They work exactly as if the staff carried on: line, space, line, space, each one the next letter. Ledger lines are drawn only as far as the note needs, never with extra lines beyond it.

Middle C in both clefs

The most important ledger-line note is middle C, written C4 in scientific pitch notation. In treble clef it sits on the first ledger line below the staff, one step below the D that hangs under the bottom line. In bass clef it sits on the first ledger line above the staff, one step above the B in the space on top. Both spellings mean the same key on the piano, the C nearest the middle of the keyboard. With A4 tuned to 440 Hz, middle C vibrates about 261.63 times a second.

The number after the letter tells you the octave, and it changes at every C, not at A. So the white key just below middle C is B3, and the one above is D4. Below the bass staff, the first ledger line is E2 and the second is C2. Above the treble staff, the first ledger line is A5 and the second is C6. Counting ledger lines is slow, so learn a few of these by sight: C4 with one line in either clef, A5 above treble and E2 below bass.

Scientific pitch notation counts octaves from C. A full 88-key piano runs from A0 at the bottom to C8 at the top, so its lowest C is C1 and middle C is the fourth C from the left. Every C on the keyboard starts a new octave number, and every note from that C up to the next B shares the number.

Why composers avoid too many ledger lines

Three or four ledger lines are still readable. Beyond that the eye loses count, so writers switch clef or use the sign 8va, meaning "play an octave higher than written". Guitar music uses a treble clef that sounds an octave lower than written so that guitarists can read without endless lines below the staff. Different clefs exist partly for this reason: each one keeps a voice or instrument mostly inside the five lines.