Introduction
The Green Screen Size Calculator computes the minimum physical dimensions of a green screen needed to fill your camera frame completely, including additional coverage for pan and tilt camera moves. Enter the camera sensor size, focal length, camera-to-subject distance, subject dimensions, pan and tilt movement in degrees, and a safety margin percentage. The tool outputs minimum screen width and height in metres and feet, frame coverage without moves, additional coverage added by pan and tilt moves, field of view angles, subject fill percentage, and the recommended minimum subject-to-screen distance for spill prevention.
What This Tool Calculates
Using a green screen that is too small for your lens and camera move results in green screen edges appearing in the frame, which forces either renting a larger screen on the day (often impossible at short notice), cropping the shot and losing coverage, or expensive digital screen extension in post-production. Understanding the precise dimensions required before the shoot eliminates these problems entirely. The calculation is particularly important for wide-angle lenses and long camera moves, which require significantly more screen coverage than narrow lenses on static shots.
The Formula and How It Works
Horizontal field of view is calculated as: 2 x arctan(sensor width / (2 x focal length)). The frame coverage at subject distance is: 2 x distance x tan(HFOV/2). Pan movement adds additional coverage equal to: 2 x distance x tan(pan degrees / 2). The minimum screen width is the sum of frame coverage plus pan coverage, multiplied by a safety margin (default 30 percent) to account for lighting falloff at screen edges, spill guard allowance, and tolerance for camera repositioning. The same calculation applies vertically for tilt movement and screen height.
Real-World Examples
Example: Full-Body Green Screen for a 35mm Lens
A full-body shot of a standing actor (1.8 m wide, 2 m tall) on a Super 35 sensor camera at 35mm focal length, 3 metres camera-to-subject distance, with a 20-degree pan move requires a minimum screen width of approximately 4.5 to 5 metres and a minimum height of approximately 3.5 metres including the 30 percent safety margin. Without the pan move, the minimum width would be approximately 3 metres. This demonstrates why camera moves more than double the screen size requirement and must be accounted for in pre-production when ordering or rigging the green screen.
Subject-to-Screen Distance for Spill Prevention
| Detail | Value |
|---|---|
| Green screen spill occurs when green light reflects from the screen onto the subject's skin, hair, and clothing, creating a colored fringe that is difficult to remove in post. | |
| The recommended minimum subject-to-screen distance is 1.5 times the subject's height. | |
| For a standing actor 2 metres tall, this means keeping the screen at least 3 metres behind the subject. | |
| This distance also allows the screen to be lit independently of the subject, which is essential for achieving an even, well-exposed screen surface. | |
| Adequate subject-to-screen distance is the single most important factor in obtaining a clean, pull-able key.. |
Pro Tips and Common Mistakes
Pro Tips
- Rent or build the screen 20 to 30 percent larger than the calculated minimum.
- Shoots almost always encounter unexpected wider lens choices or spontaneous camera moves that were not in the original shot list.
- Shoot the screen between 1 and 1.5 stops brighter than the subject's key light level using dedicated screen lights such as Kino Flo Chroma units or LED panels with green gel.
- Avoid wrinkles in fabric screens by hanging the screen from a spreader bar with significant overhang and weighting the bottom.
Common Mistakes
- The most common mistake is shooting with the actor too close to the screen, creating unremovable green spill on their hair and shoulders.
- The second most common mistake is using wrinkled, poorly lit, or under-sized screens that produce uneven luminance and dark areas that resist keying.
- Shooting under mixed lighting (daylight and tungsten) without matching both the screen lights and the subject key light to the same color temperature makes the key inconsistent.
Frequently Asked Questions
What color is better for chroma key, green or blue?
Green is more common in digital production because digital camera sensors have higher sensitivity in the green channel, providing a cleaner, less noisy key. Blue screen is preferred when the subject has green elements (clothing, eyes, props) or when shooting in daylight environments where ambient sky light is already blue, reducing the lighting requirement for the screen.
How far should the subject be from the green screen?
At minimum 1.5 times the subject's height to prevent green spill. For a standing actor 1.8 metres tall, this means at least 2.7 metres of separation between the actor and the screen. Greater distance is always better for spill prevention and allows independent lighting of screen and subject.
What is a clean plate and why do I need it?
A clean plate is a take of the background without the subject in frame. It allows compositors to use background subtraction keying techniques and to repair areas of the key where the subject's edges are difficult to isolate. Always shoot clean plates for every green screen setup, ideally at the beginning and end of the shooting period to capture any lighting changes.
Start Calculating
Use the calculator above to run your numbers before your next production.
