Voting power is the share of the total votes that a holder can cast on matters such as electing directors or approving a merger. It is worked out by multiplying the number of shares by the votes each share carries, and dividing by the total votes available.
It can differ sharply from economic ownership. In a company with two classes of shares, a founder who owns 15 percent of all the shares may control a majority of the votes if their shares carry ten votes each. Investors who own most of the economic value may have little say.
Voting power matters for takeovers, governance and shareholder proposals. It is also the test used to decide whether a company counts as controlled.
In the ownership tables of a prospectus or proxy statement, compare the percentage of shares owned with the percentage of voting power for each major holder, and note which holders act together.