Formula for dimension for change of base field of algebraic group

Definition
Suppose $$L$$ is a field extension of a field $$K$$ of degree $$d$$. Suppose $$G$$ is a algebraic group over $$L$$ such that the dimension of the group over $$L$$ is $$m$$. Then, under the natural structure of $$G$$ as an algebraic group over $$K$$, the dimension over $$K$$ is the product $$md$$.