WAV stores audio uncompressed, which is why recorders, audio interfaces and editing software use it, and why the files are so large: CD quality stereo runs to about 10 MB per minute, so an hour of recording is around 600 MB. MP3 at 320 kbps takes about 2.4 MB per minute, a reduction of roughly three quarters, and at 192 kbps it is closer to 1.4 MB per minute. That is the difference between a file you can email or upload and one you cannot. This page opens with MP3 as the output and 320 kbps selected, because a WAV source is lossless and deserves the best MP3 can do; drop the files and convert. For speech, such as interviews, lectures and podcasts, 128 kbps is plenty and makes files even smaller. Keep the WAV as your master if you might edit it later, since every lossy export throws away information that cannot be recovered, and editing an MP3 then exporting it again compounds the loss. Large WAV files take a little time because the converter runs in your browser; files are processed one at a time and each shows its own status. To go the other way use MP3 to WAV Converter, and for lossless compressed albums see FLAC to MP3 Converter.
The split that matters most in audio formats is lossy against lossless. A lossless format such as WAV or FLAC stores enough information to reconstruct the original waveform exactly, which is why WAV files run around 10MB per minute of stereo CD quality audio. Lossy formats such as MP3, OGG Vorbis, AAC, and Opus use psychoacoustic models to discard sound that listeners are unlikely to perceive, typically hitting a tenth of the size for audio most people cannot distinguish in normal listening. The important consequence is that the discarded information is gone permanently. Converting MP3 to WAV inflates the file back to full size without recovering anything, and each further lossy conversion compounds the loss, an effect known as generation loss. The practical rule is to keep a lossless master and export lossy copies from it, rather than converting between lossy formats repeatedly. Bitrate is where quality and size are actually traded. At 128 kbps most listeners cannot reliably distinguish MP3 from the source on laptop speakers or earbuds, though the gap becomes audible on good headphones with dense music. At 256 to 320 kbps MP3 is effectively transparent for nearly everyone. OGG Vorbis reaches similar quality at a somewhat lower bitrate, because it is a newer design than MP3, and Opus does better still, which is why messaging apps and voice chat use it. Sample rate and bit depth apply to the uncompressed side. This tool writes WAV at 16 bit and 44.1 kHz, the CD standard, which is the format editing software and mastering workflows expect, and which every audio application on every platform can open without conversion.