How does auction design affect the division of surplus among buyers? We propose a parsimonious measure for equity and apply it to multi-unit auctions, in which unit demand buyers with private-common values pay mixtures of uniform and pay-as-bid pricing. We show that uniform pricing is equity-optimal if and only if buyers have a pure common value. Surprisingly, however, with pure private values, pay-as-bid pricing may not be optimal, and uniform pricing can achieve higher surplus equity. For the class of log-concave signal distributions, we provide prior-free bounds on the equity-optimal pricing rule.