"If it can be written, or thought, it can be filmed..." STANLEY KUBRIC
From Encyclopedia PRO
There is no unique "rule" for the writing of a screenplay, but throughout the world, within the relevant industries, several conventions are withheld and adhered to.
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 format known widely as 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 the 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. This rule of thumb is widely contested -- a page of dialog 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. Most experienced readers of screenplays can judge simply by weight and thickness whether the screenplay is 'too long' or 'too short'.
After weighing it in the hand, the next act of a harried reader or executive will be to flick to the last page to see the page count. Ideally a screenplay should be 90-120 pages long. Comedies and children's films tend to weigh in at the lower end. It is a common misconception that a screenplay 'should' be 120 pages long; in fact 120 pages is at the very top of the acceptable range for most purposes. 110-115 pages is usually better in the mind of most executives. Anything more than 120 pages will set off alarm bells unless there is a substantial balancing factor (for example, James Cameron is attached to direct).
Most experienced readers can tell instantly whether a script is in standard studio format or not simply by looking at a couple of pages. If it is not, they will assume that the writer is inexperienced and may not read any further. Therefore it is important to know the rules.
Unfortunately, there is no single canonical standard for 'studio format' although the definitions of the format are mostly very similar. 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 useful and accurate guide to screenplay format. A more detailed reference is The Complete Guide to Standard Script Formats (Cole and Haag, SCB Distributors, 1980, ISBN 0929583000). Most screenwriting software comes with a set of templates for various screenplay formats which are more or less standard.
Screenplays are almost always written using a monospaced font, often a variant of Courier although other fonts are sometimes seen, including special bitmapped fonts intended to resemble the output of an old battered typewriter such as a Remington Portable.
Detailed computer programs designed specifically for screenplays, but that also have templates for teleplays and stageplays, are Movie Magic, Montage and Final Draft. These are the industry standards for professional screenwriters. An open source (free) option is also available: Celtx is designed for screenplays and collaborations, and useful for teleplays and stageplays. Furthermore, screenwriting software for handheld devices (Palm OS, and Windows Mobile / Pocket PC) is also available with ScriptRight Mobile Edition.
For American TV shows, the format rules for hour dramas, like CSI, and single-camera sitcoms, like Scrubs, are essentially the same as for motion pictures. The main difference is that TV scripts have act breaks. Multi-camera sitcoms, like Two and a Half Men, use a different, specialized format that derives from radio and the stage play. In this format, dialogue is double-spaced, action lines are capitalized, and scene headings are capitalized and underlined.
The script format for documentaries and audio-visual presentations which consist largely of voice-over matched to still or moving pictures is different again and uses a two-column format which can be particularly difficult to achieve in standard word processors, at least when it comes to editing.
American screenplays are printed single-sided on three-hole-punched letter sized (8.5 x 11 inch) paper, and held together with an industry standard of not three but two brass brads. In the UK, double-hole-punched A4 paper is often used, although some UK writers use the US letter paper format, especially when their scripts are to be read by American producers, since otherwise the pages may be cropped when printed on US paper. Despite the use of double-punched paper, it is common to see scripts in the UK held together by a single brad punched in the top left hand corner. This makes it easy to flip from page to page during script meetings and may have something to do with the taller page of A4.
Screenplays are usually bound with a light card stock cover and back page, often showing the logo of the production company or agency submitting the script. Writer's scripts are usually bound in a plain red or blue cover.
Increasingly, reading copies of screenplays (that is, those distributed by producers and agencies in the hope of attracting finance or talent) are distributed printed on both sides of the paper to cut down on their bulk, and occasionally they are reduced to half-size to make a small book which is convenient to read or put in a pocket. However, writers should generally submit on single sided, full sized paper and leave the way the script is reproduced up to the agency or producer.
Although most writing contracts continue to stipulate physical delivery of three or more copies of a finished script, it is extremely common for scripts to be delivered electronically via email. Although most production companies can handle scripts in Final Draft, Movie Magic or MS Office format, it is better practice to supply scripts as a PDF file where possible. This is because it gives the writer final control over the layout of the script, which may otherwise vary depending on what fonts and/or paper size the recipient uses to print the script out. DreamaScript produces multiple formats of screenplays, including PDF.
A detailed description of correct screenplay format can be found here.