The throw ratio of a projector is a crucial specification that determines how far away from the screen the projector needs to be placed to achieve a specific image size. It's a simple ratio that helps installers and home theater enthusiasts position their projectors correctly for optimal viewing.
The formula for throw ratio is as follows:
Throw Ratio = Throw Distance / Screen Width
In this calculator, the Throw Distance is the distance from the projector's lens to the screen, and the Screen Width is the horizontal dimension of the desired projected image. It's essential to use consistent units for both measurements (e.g., both in inches, both in feet, both in centimeters, or both in meters).
Why is Throw Ratio Important?
Placement Flexibility: Projectors have different throw ratios, meaning some need to be placed far away for a large image (long throw), while others can be placed very close (short throw or ultra-short throw). Knowing the throw ratio helps you choose a projector that fits your room dimensions.
Image Size Control: The throw ratio, along with the projector's lens, dictates the range of image sizes you can achieve at different distances.
Avoiding Obstructions: In dedicated home theaters or conference rooms, understanding the throw ratio ensures the projector can be placed without obstructing seating or causing installation challenges.
Keystone Correction: While some projectors offer keystone correction to square up the image if placed off-axis, relying heavily on it can degrade image quality. Proper placement using the throw ratio is always preferred.
How to Use the Calculator:
Measure the width of your screen or the desired width of your projected image.
Measure the distance from the projector lens to the screen. Ensure both measurements use the same units (e.g., both in inches, or both in feet, or both in centimeters, or both in meters).
Enter these values into the respective fields above.
Click "Calculate Throw Ratio".
The calculator will display the throw ratio. For example, a throw ratio of 1.5 means that for every 1.5 units of distance, the screen width will be 1 unit. So, if the screen width is 5 feet, the projector needs to be 7.5 feet away (5 * 1.5 = 7.5).
Example: If your screen width is 100 inches and your projector is placed 120 inches from the screen, the throw ratio is 120 / 100 = 1.2. If your screen width is 8 feet and your projector is 15 feet away, the throw ratio is 15 / 8 = 1.875.
function calculateThrowRatio() {
var screenWidthInput = document.getElementById("screenWidth");
var throwDistanceInput = document.getElementById("throwDistance");
var resultValueDiv = document.getElementById("result-value");
var screenWidth = parseFloat(screenWidthInput.value);
var throwDistance = parseFloat(throwDistanceInput.value);
// Clear previous error messages or results
resultValueDiv.textContent = "–";
resultValueDiv.style.color = "var(–success-green)";
// Validate inputs
if (isNaN(screenWidth) || screenWidth <= 0) {
resultValueDiv.textContent = "Invalid screen width";
resultValueDiv.style.color = "red";
return;
}
if (isNaN(throwDistance) || throwDistance <= 0) {
resultValueDiv.textContent = "Invalid throw distance";
resultValueDiv.style.color = "red";
return;
}
// Calculate throw ratio
var throwRatio = throwDistance / screenWidth;
// Display the result
// Format to a reasonable number of decimal places, e.g., 3
resultValueDiv.textContent = throwRatio.toFixed(3);
}