Described is a method and system by which a computer program window is sized based on the content to display. The window may automatically resize itself as content changes. When laying out an element tree of elements that contain the content, the elements provide desired size information to a parent container, and so on, up to the root element (e.g., a window). If a window property is set to size to the content, a window size is computed during layout, having a height and/or width based on the child elements plus X and Y deltas for a window non-client area and borders. Logic attached to window message handling controls changes to the content/window, such as to automatically resize for changed content, and to selectively turn off or persist the size to content property. Sizing to content may be programmatically limited to one dimension, with the other dimension fixed.