# What is my projector throw distance?

Works out how far a projector must sit from the screen for a given image size, from its throw ratio and the aspect ratio, with the range for a zoom lens.

- Page: https://www.acalculator.org/everyday-life/projector-throw-calculator
- JSON spec: https://www.acalculator.org/everyday-life/projector-throw-calculator.json
- Version: 16aa45482580

## Default answer

Example with the default inputs (Throw ratio 1.5, Image size (diagonal) 100 in, Image aspect ratio 16:9): A 100 in image at a throw ratio of 1.5 needs a throw distance of 10.89 ft.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| tr | Throw ratio | Distance ÷ image width, from the projector’s specs; 1.5 is common. |
| tr2 | Throw ratio, long end of zoom | Optional: for a zoom lens listed as 1.5 to 2.0, the larger number. |
| d | Image size (diagonal) | The picture you want, corner to corner; a screen’s size. |
| ar | Image aspect ratio | 16:9 for most home projectors and screens; 2.39:1 for a cinema-scope screen. |
| rw | Width | The width part of the image ratio. |
| rh | Height | The height part of the image ratio. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| distance | Throw distance | Throw ratio × image width, lens to screen. |
| distanceMax | Throw distance, long end of zoom | Long-end throw ratio × image width. |
| width | Image width | Diagonal × a ÷ √(a² + b²) for an aspect ratio a : b. |
| height | Image height | Diagonal × b ÷ √(a² + b²). |

## Method

Throw distance = throw ratio × image width; image width = diagonal × a ÷ √(a² + b²) for an aspect ratio a : b.

## Assumptions

- The distance is from the projector’s lens to the screen, with the projector square to the screen.
- The throw ratio is the maker’s figure for the image width; keystone or digital zoom changes the picture size.

## Worked examples

1. tr = 1.5, d = 2.54, ar = 16:9 gives width = 2.213802, distance = 3.320703. Source: Throw (projector), Wikipedia (throw ratio = distance from the lens to the screen ÷ screen width), https://en.wikipedia.org/wiki/Throw_(projector) (retrieved 2026-10-03).
2. tr = 2, d = 1.905, ar = 4:3 gives width = 1.524, height = 1.143, distance = 3.048. Source: Throw (projector), Wikipedia (throw ratio = distance from the lens to the screen ÷ screen width), https://en.wikipedia.org/wiki/Throw_(projector) (retrieved 2026-10-03) (a 2.0 ratio puts a 60 in wide image 120 in away).
3. tr = 1.36, tr2 = 2.18, d = 3, ar = 16:9 gives distance = 3.556028, distanceMax = 5.700104. Source: Throw (projector), Wikipedia (throw ratio = distance from the lens to the screen ÷ screen width), https://en.wikipedia.org/wiki/Throw_(projector) (retrieved 2026-10-03).

## FAQ

### What is a throw ratio?

The distance from the projector’s lens to the screen divided by the width of the image. A 1.5 ratio means the projector sits 1.5 ft back for every foot of image width.

### How do I calculate throw distance?

Multiply the throw ratio by the image width. For a 100 in 16:9 image, the width is 100 × 16 ÷ √(16² + 9²) = 87.2 in, so at a 1.5 ratio the lens sits 130.7 in (10.9 ft) from the screen.

### What does a zoom range such as 1.36 to 2.18 mean?

The zoom lens can give any throw ratio in that range, so the projector can sit anywhere between the short and the long distance for the same image size. Type both numbers to see the range.

### What is a short-throw projector?

One with a throw ratio below about 1, so it makes a large image from close up. Ultra-short-throw models are below about 0.4 and sit just in front of the wall.

### Where do I measure the distance from?

From the front of the lens to the screen. Makers’ distance tables use the lens; add the depth of the projector behind it when you plan a shelf or a mount.

## Sources

- Throw (projector), Wikipedia (throw ratio R = D ÷ W, the distance from the lens to the screen over the screen width; a 2.0 ratio and a 60 in wide screen need 120 in). https://en.wikipedia.org/wiki/Throw_(projector) (retrieved 2026-10-03)