Projector Throw Ratio Calculator
A projector's throw ratio is the fixed relationship between how far the lens is from the screen and how wide the image it makes: throw ratio = throw distance ÷ image width.
Enter Values
How to use this calculator
- Fill in exactly TWO of the three fields — throw ratio, throw distance (m) and image width (m) — and leave the one you want to find blank.
- Enter the throw ratio as the plain number a manufacturer quotes (a '1.5:1' lens is 1.5); read it from the projector's spec sheet or lens range.
- Read the emphasised answer first, then use the supporting image width, throw distance, 16:9 diagonal and throw-type label to sanity-check your room layout.
How it works
A projector's throw ratio is the fixed relationship between how far the lens is from the screen and how wide the image it makes: throw ratio = throw distance ÷ image width. Because the three quantities are locked together, knowing any two gives the third — divide distance by width for the ratio, multiply ratio by width for the distance, or divide distance by ratio for the width.
Throw ratio uses the image WIDTH, not the diagonal, so this tool also reports the diagonal you would get if the picture is a standard 16:9 shape (diagonal = width × √(1 + (9/16)²)). It labels the ratio by the usual industry bands: below about 0.4 is ultra-short throw, 0.4–1 is short throw, roughly 1–2.5 is standard throw, and above about 2.5 is long throw. Zoom lenses cover a RANGE of ratios, so treat a single figure as one setting within that range.
Worked example
How far to place a 2 m wide image with a 1.5 throw ratio. You have a projector with a fixed throw ratio of 1.5 and want a 2 m wide image. Enter throw ratio = 1.5 and image width = 2, leaving throw distance blank. Throw distance = throw ratio × image width = 1.5 × 2 = 3 m, so the lens must sit 3 m from the screen. For a 16:9 image the diagonal works out to about 2.294 m (≈ 90 inches), and a 1.5 throw ratio is a standard-throw projector.
Common mistakes
- Using the screen DIAGONAL as the image width. Throw ratio is defined against width, so a 100-inch 16:9 screen is only about 87 inches (2.21 m) wide — plug in the width, not the diagonal.
- Mixing units. Enter both throw distance and image width in metres; a distance in metres and a width in centimetres will give a ratio 100× off.
- Treating a zoom projector as a single throw ratio. Zoom lenses quote a range (e.g. 1.4–2.8:1); the distance you calculate is only valid at the specific ratio you enter, so check it falls inside the lens's published range.
Frequently asked questions
What is a projector throw ratio?
It is the ratio of the throw distance (lens-to-screen) to the width of the projected image: throw ratio = distance ÷ image width. A 1.5:1 projector 3 m away makes a 2 m wide picture. It is a fixed property of the projector and lens, so it lets you work out placement before you buy or hang the unit.
Is throw ratio based on image width or diagonal?
Always the width. Screen sizes are usually quoted as a diagonal, so you must convert: for a 16:9 image the width is the diagonal × 0.8716. This tool works in width and additionally shows the 16:9 diagonal for reference so you can match it back to a quoted screen size.
What counts as short throw or long throw?
As a rough industry guide: ultra-short throw is under about 0.4, short throw is about 0.4 to 1, standard throw is about 1 to 2.5, and long throw is above about 2.5. Lower ratios let a projector sit close to the screen (good for small rooms and avoiding shadows); higher ratios suit rear-of-room or ceiling mounts in larger spaces.
Does this account for zoom lenses and offset?
No. It solves the single throw-ratio relationship only. Zoom lenses cover a range of ratios, and vertical/horizontal lens shift (offset) affects where the image lands but not its size. Confirm the calculated distance sits within your lens's published zoom range and use the manufacturer's projection calculator for exact mounting and offset.
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