Instructions

You must enter a base ratio first (Width and Height) to know from which resolution the calc has to make the resize (The default value is 1280x720, that it's a 16:9 valid resolution).

Then, you enter in the Result Ratio box the Width/Height that you want to resize, and it calcules the other Height/Width automatically.

It tells you exactly what kind of resolution you chosed, and if it is a 16:9 or 4:3 resolution.

If you make the resize for a video encoding, there is a table that tells you if the Result Ratio is a mod16/8/4/2 compliant resolution (because there are many softwares like AviSynth that only supports mod compliant). If it's not, it makes the respectively correction (always upscaling it to prevent loss of footage) of Width/Height automatically. With that, you can know how many pixels you need to crop if you want that mod compliant.

One recommendation that maybe you want to know is that the mod16 encoding have better results than the other mods. But it's not strictly necessary since x264 supports mod8/4/2 too.