Every conversion, and what it costs you.
Each page runs the conversion in your browser and states plainly what the target format cannot carry, which settings are used, and when you should not convert at all.
Image
15 conversionsJPG to PNG
This cannot recover detail.
JPG to WebP
The usual reason to do this is page weight.
PNG to JPG
PNG transparency has nowhere to go in a JPG, so Filoven composites the image onto a white background before encoding rather than producing black fringes..
PNG to WebP
WebP keeps the alpha channel, so this is the one conversion that shrinks a transparent PNG without flattening it.
WebP to JPG
Two lossy codecs in sequence.
WebP to PNG
The common reason is software that refuses to open WebP.
AVIF to JPG
AVIF can hold HDR and wide colour that JPG cannot represent, so bright highlights may flatten.
AVIF to PNG
The compatibility escape hatch for AVIF: PNG opens in every editor written in the last twenty years and keeps the alpha channel intact..
AVIF to WebP
Both are modern web codecs; the reason to move is browser support in older Safari and Edge builds.
BMP to JPG
Worth doing only for photographic BMPs, usually scanner or old camera output.
BMP to PNG
BMP stores pixels essentially uncompressed, so this is the conversion with the largest size drop of any on the site.
BMP to WebP
The biggest single size reduction available here: uncompressed pixels to a modern lossy codec, routinely a 95 percent drop..
GIF to JPG
GIF's flat colour blocks are the worst case for JPEG, which was built for photographs.
GIF to PNG
A GIF is capped at 256 colours, and PNG is not, but converting does not add colours back.
GIF to WebP
WebP is the only common web format that can hold both animation and transparency, which is why it replaces GIF rather than merely competing with it..
Audio
16 conversionsFLAC to MP3
FLAC is lossless, so this is the first quality loss the file has taken.
M4A to MP3
Two lossy codecs in sequence, so the result is slightly worse than the M4A at a slightly larger size.
MP3 to WAV
Editors, DAWs and hardware samplers want PCM.
WAV to MP3
The classic size conversion.
AAC to MP3
A raw AAC stream has no container, so tags and cover art are usually absent to begin with.
FLAC to M4A
The usual reason is fitting a lossless library onto a phone.
FLAC to WAV
The only genuinely lossless conversion in the audio set.
M4A to WAV
This does not restore what AAC discarded.
MP3 to M4A
AAC is the better codec, but re-encoding an MP3 into it cannot recover what MP3 removed.
MP3 to OGG
Transcoding between two lossy codecs always costs quality.
OGG to MP3
Vorbis is the better codec at low bitrates, but MP3 is the one that plays in car stereos and older hardware.
OGG to WAV
Usually done to get game or Unity audio assets into an editor, since OGG is the standard shipping format for game sound and PCM is what tools expect..
Opus to MP3
Opus is what WhatsApp and Discord voice notes actually are.
WAV to M4A
The right way to get audio into the Apple ecosystem: one lossy step from an uncompressed master, in the codec iOS and macOS handle natively..
WAV to OGG
This one is worth doing from a WAV master: it is the first and only lossy step, so Vorbis performs at its best..
WMA to MP3
WMA is effectively a dead format outside old Windows software, which makes this a one-way migration most people only do once, in bulk..
Video
11 conversionsAVI to MP4
AVI files are usually old, and old AVI codecs are what modern players choke on.
MKV to MP4
MKV commonly carries several audio tracks and subtitle tracks.
MOV to MP4
iPhone video is MOV, and MOV is often just H.264 in a different container.
WebM to MP4
WebM plays in browsers and almost nowhere else.
AVI to WebM
Old footage to modern web video in one step.
FLV to MP4
FLV is Flash-era video, and no current browser can play it.
MKV to WebM
Both are Matroska containers underneath, but WebM restricts what is allowed inside, so the video and audio are re-encoded to VP9 and Opus rather than copied..
MOV to WebM
The path from iPhone footage to a self-hosted web video.
MP4 to AVI
This is a downgrade, and the only honest reason to do it is old hardware, usually a DVD player or an industrial display that reads AVI only..
MP4 to MOV
Mostly done for Final Cut and QuickTime workflows.
WMV to MP4
WMV predates every phone in your pocket.
Data
8 conversionsCSV to Excel
The real benefit is that Excel stops guessing.
CSV to JSON
Every CSV value is text.
Excel to CSV
Formulas are exported as their last calculated value, not the formula.
JSON to CSV
CSV is flat and JSON is not.
JSON to YAML
The usual reason is readability: the same structure as YAML is roughly 30 percent fewer characters and no bracket matching..
XML to JSON
XML distinguishes attributes from child elements and JSON does not, so attributes are mapped into keys.
YAML to JSON
YAML comments do not exist in JSON and are silently dropped.
JSON to XML
JSON arrays have no direct XML equivalent, so each item becomes a repeated element.
Document
4 conversionsHTML to Markdown
Styling and scripts have no Markdown equivalent and are discarded.
Markdown to HTML
The output is a fragment, not a page: headings, lists, links and code blocks, with no stylesheet or wrapper.
Word to HTML
Word's own HTML export is notoriously bloated with mso- styles.
Word to Plain text
Everything except the words is removed: formatting, images, tables, comments and tracked changes.