Projector throw distance calculator: screen size and distance
Find the image size your space can hold, or work backward from the screen you want. Use the throw ratio from your projector manual. No model lookup or account needed.
Plan your projection
Your projection estimate
- Image width
- Image height
- Image diagonal
- Lens-to-screen distance
Diagrams show the low throw-ratio endpoint: largest image at a fixed distance, or shortest distance for a fixed diagonal. Dashed lines mark entered room limits in the top view. Side view is centered only to illustrate image height; it does not specify lens offset, mounting height or eye level.
Calculations run in your browser. This calculator does not store or send your measurements.
This is a geometry estimate, not an installation plan. Allow for the screen frame, projector body, cables and ventilation. Wall height is not checked. Lens shift, keystone correction, digital zoom, letterboxing and ultra-short-throw placement geometry are not modeled. Confirm final placement and image-format assumptions in the manual before mounting.
How it's calculated
- Width = distance ÷ throw ratio
- Height = width ÷ aspect ratio
- Diagonal = √(width² + height²)
- For a target diagonal: width = diagonal ÷ √(1 + 1/aspect ratio²)
- Distance = width × throw ratio
For a fixed distance, the largest throw ratio gives the smallest image. For a fixed diagonal, multiply its width by each endpoint of the throw-ratio range to get the minimum and maximum lens distances. Use matching units for every length.
120 inch screen distance: a worked example
A 120-inch diagonal at 16:9 is approximately 104.59 inches wide and 58.83 inches high. With an illustrative throw ratio of 1.2–1.5, the lens distance is 125.51–156.88 inches (10.46–13.07 ft, or 3.19–3.98 m). Your projector may require a different ratio. This is projector distance, not seating distance.
Projector distance questions
How far should a projector be from the screen?
Multiply the image width by the throw ratio listed in your projector manual. Measure from the lens to the screen surface. If the manual gives a zoom range, the two ratios give the minimum and maximum distances.
How far away should a projector be for a 120 inch screen?
There is no single distance for every projector. At 16:9, a 120-inch diagonal has a width of about 104.59 inches. Multiply that width by your projector’s throw ratio; for the illustrative range 1.2–1.5, the lens distance is 125.51–156.88 inches.
Where do I find the throw ratio, and does room fit guarantee installation?
Look for throw ratio or a projection-distance chart in the projector manual or manufacturer specifications. A room-fit result checks only the dimensions you enter. It does not confirm mounting height, lens shift, projector-body clearance or compatibility with a particular screen.
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