1 : related in size, number, or amount to (something else) Your share of the profits will be in proportion to the amount of work that you do.

Is proportion plural or singular?

Proportion is singular, so have is correct.

Does proportion mean share?

Proper or equal share. Etymology: From proporcion, from proportion, from proportio, from pro + portio; see portion. The relation of one part to another or to the whole with respect to magnitude, quantity, or degree.