I didn't like any of the Screen Resolution / DPI calculators... so I made a better one:

https://dpi.froods.ca

Updated Features:

- Type in what you know, it calculates everything it can automatically.

- Canned values, in case you forgot what "WSXGA+" is.

- Calculates how wide a TV for a certain Field of View + Distance.

- Creates a convenient text string.

- Push calculated outputs back into input.

- Run in Mixed units, Metric, or Imperial.

- Ratio visualizer.

- Size visualizer.