Converticon is a free online utility to convert your PNG image files to ICO files. It results in a lossless conversion, and lets you export the converted ICO file in multiple sizes. The whole process is completed online, and you do not need to download or install anything.
To start the conversion process, just upload your PNG file. Converticon will immediately convert that to ICO file. You can export the converted file in following sizes:
You can also export the converted ICO file in the original size.
If you are looking to quickly convert your PNG file to ICO without installing anything, Converticon is a good option. It is totally free. If you need some full fledged converter, you can try Photoscape or Inkscape. Try Converticon.