This rule of thumb is widely contested — a page of dialogue usually occupies less screen time than a page of action, for example, and it depends enormously on the literary style of the writer — and yet it continues to hold sway in modern Hollywood. Some studios have definitions of the required format written into the rubric of their writer's contract.
The Nicholl Fellowship, a screenwriting competition run under the auspices of the Academy of Motion Picture Arts and Sciences, has a guide to screenplay format.
Motion picture screenplays intended for submission to mainstream studios, whether in the US or elsewhere in the world, are expected to conform to a standard typographical style known widely as the studio format which stipulates how elements of the screenplay such as scene headings, action, transitions, dialog, character names, shots and parenthetical matter should be presented on the page, as well as font size and line spacing.
One reason for this is that, when rendered in studio format, most screenplays will transfer onto the screen at the rate of approximately one page per minute.
The middle hole is left empty as it would otherwise make it harder to quickly read the script.
In the United Kingdom, double-hole-punched A4 paper is normally used, which is slightly taller and narrower than US letter size.
Unique to the screenplay (as opposed to a stage play) is the use of slug lines.
A slug line, also called a master scene heading, occurs at the start of every scene and typically contains three pieces of information: whether the scene is set inside (interior/INT.) or outside (exterior/EXT.), the specific location, and the time of day. In a "shooting script" the slug lines are numbered consecutively for ease of reference.
Multi-camera sitcoms use a different, specialized format that derives from stage plays and radio.
In this format, dialogue is double-spaced, action lines are capitalized, and scene headings, character entrances and exits, and sound effects are capitalized and underlined.