Ten to twenty times bigger. Not one bit better. Here's why you'd still do it.
Unpacking an MP3 into WAV can't restore what the MP3 discarded. But plenty of tools only accept WAV, and editing uncompressed audio avoids further loss. Tell us where it's going and we'll match the exact format it wants.
Open songs, voice memos or old archives and save them as MP3, AAC, FLAC, Opus, WMA, AC3, AMR or any of 19 more. Pick a quality preset or an exact bitrate, convert the whole batch in one pass, then download each file or one ZIP.
ffmpeg -i input.wav -vn -map_metadata 0 -ar 48000 -ac 2 -c:a libmp3lame -b:a 192k -f mp3 output.mp3Each time you trim, fade or level an MP3 and save it as MP3 again, it's encoded again, and each encode throws away a little more. Convert to WAV once, do all your edits, then export a single MP3 at the end.
“WAV” covers many settings. A file at the wrong sample rate can be rejected or play at the wrong speed.
44.1 kHz · 16-bit · stereoThe Red Book CD standard. Burning software rejects anything else, or silently resamples it.48 kHz · 24-bitVideo runs at 48 kHz. Matching it avoids a hidden resample on every playback of the timeline.8 kHz · 8-bit µ-law · monoTelephone networks carry only up to ~3.4 kHz. Many hold-music and menu systems require this exact format.16 kHz · 16-bit · monoSpeech-recognition engines work at 16 kHz mono. Higher rates just make the upload bigger.44.1 kHz · 16-bitHardware samplers often only read uncompressed WAV. Check the manual for mono/stereo limits.48 kHz · 24-bit · BWFBroadcast Wave adds timestamps and metadata to a standard WAV for playout systems.An MP3 stores a compact description of the sound. A WAV writes out every single sample, 44,100 of them per second, per channel, whether or not anything is happening. Silence costs as much space as a full orchestra.
Most WAVs made from MP3s are a stop on the way to something else.