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Projector Throw Distance Calculator

Uses a projector's throw ratio (distance ÷ image width) to find the projection distance for a given screen width, or the image width for a given distance, and reports the image height and diagonal for the chosen aspect ratio.

When to use

You are placing a projector or choosing a screen size and know the lens throw ratio from the spec sheet, or want to know what throw ratio a room needs.

Do not use when: You need TV seating distances (use tv-viewing-distance) or lens-shift/keystone geometry; zoom lenses have a throw-ratio range, so run the calculator at both ends.

Formula

throw_ratio = distance / width; distance = throw_ratio × width; width = distance / throw_ratio; height = width / aspect; diagonal = √(width² + height²); 1 m = 39.3701 in

Throw ratio is measured from the lens to the screen surface; for zoom lenses use the minimum and maximum ratios from the data sheet. Ultra-short-throw projectors quote the ratio from the lens exit, typically 20–40 cm behind the front of the unit.

Inputs

Parameter	Type	Unit	Required	Description
`throw_ratio`	number		yes	Lens throw ratio = throw distance / image width (e.g. 1.5 means 1.5 m of distance per metre of width; 0.25 for an ultra-short-throw). Range: ≥ 0.1, ≤ 20
`screen_width_m`	number	m	no	Desired image width. Give this to get the throw distance (takes precedence over throw_distance_m). Range: > 0, ≤ 100
`throw_distance_m`	number	m	no	Lens-to-screen distance. Give this alone to get the image size; with the width it also yields the throw ratio the room needs. Range: > 0, ≤ 200
`aspect_ratio`	enum: 16:9 \| 16:10 \| 4:3 \| 2.35:1		default 16:9	Width-to-height ratio of the screen or image.

Outputs

Output	Type	Unit	Description
`throw_distance_m`	number	m	Lens to screen = throw_ratio × width.
`throw_distance_ft`	number	ft	Same distance in feet.
`screen_width_m`	number	m	Projected image width.
`screen_height_m`	number	m	width / aspect ratio.
`screen_diagonal_m`	number	m	√(width² + height²).
`screen_diagonal_in`	number	in	Diagonal in inches, as screens are sold.
`required_throw_ratio`	number		throw_distance_m / screen_width_m when both are given, to compare with the lens.
`throw_type`	string		Ultra short throw (<0.4), short throw (0.4–1), standard (1–2) or long throw (>2).

Example

Throw ratio 1.5, 2 m wide 16:9 image: {"throw_ratio":1.5,"screen_width_m":2} → {"throw_distance_m":3,"throw_distance_ft":9.84,"screen_width_m":2,"screen_height_m":1.125,"screen_diagonal_m":2.295,"screen_diagonal_in":90.3,"throw_type":"Standard throw"}

Throw ratio 1.2 at 4 m, 16:9: {"throw_ratio":1.2,"throw_distance_m":4} → {"throw_distance_m":4,"screen_width_m":3.333,"screen_height_m":1.875,"screen_diagonal_m":3.824,"screen_diagonal_in":150.6}

GET https://tttkmbb.com/api/v1/calculate/projector-throw?throw_ratio=1.5&screen_width_m=2

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/projector-throw (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/projector-throw · Markdown: https://tttkmbb.com/everyday/projector-throw.md · JSON definition: https://tttkmbb.com/everyday/projector-throw.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="projector-throw"
OpenAPI operationId: calculate_projector_throw_distance
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

Throw (projector) – throw ratio definition (Wikipedia) (reference)
Projector Central – Projection calculator (throw distance) (reference)

FAQ

Where is the throw ratio on a spec sheet?

Usually as a range such as '1.32–1.72:1' for zoom lenses; the first number is the widest image from a given distance, the second the most zoomed-in.

Does the ratio use width or diagonal?

Width. Distances quoted per inch of diagonal depend on the aspect ratio, which is why this calculator asks for it.

Related calculators

TV Viewing Distance Calculator — Seating distance for the resulting image size.
Aspect Ratio Calculator — Image dimensions from a ratio.
Screen PPI Calculator — Pixel density of a display of that size.