Described is a layout system and process for user interface elements of computer programs. The layout system generally refers to a protocol and associated API that enables sizes and positions to be allotted, in which user interface elements are rendered. The layout system may be split between a core layout system and a framework layout system. The core provides minimal policy/rules that are imposed to allow flexibility for a given framework implementation. The framework adds support for user-specified sizing, positioning, margins, minimum sizes, maximum sizes and specific layout elements. Parent elements (e.g., containers) direct measure calls and arrange calls to child elements. The layout system essentially intercepts those calls and depending on policy may manipulate the properties of those calls for sizing, positioning, alignment and the like to ensure uniform and consistent layout results.