jmc

The area of the 10-inch pizza is $5^2\pi =25\pi$ square inches, while the area of the 12-inch pizza is $6^2\pi =36\pi$ square inches. The increase is $36\pi -25\pi =11\pi$. As a factor, this is an increase of $\frac{11\pi }{25\pi }=\frac{44}{100}=\boxed{44\%}$.