The number of beats in a measure depends on the time signature of the piece of music. However, in common time signatures:
- 2 (e.g., 2/4) has 2 beats in a measure.
- 3 (e.g., 3/4) has 3 beats in a measure.
- 4 (e.g., 4/4) has 4 beats in a measure.
- 8 (e.g., 6/8 or 9/8) typically has more complex groupings.
Given the provided options, the most common number of beats in a measure in Western music is 4 (for 4/4 time).
So, the answer is 4.