The formula to calculate the volume of a sphere is:
\[ V = \frac{4}{3} \pi r^3 \]
where:
- \( V \) is the volume,
- \( \pi \) is a mathematical constant (approximately 3.14159),
- \( r \) is the radius of the sphere.
The missing part of the formula that you're looking for is likely \( \frac{4}{3} \pi r^3 \).