BMP to AVIF Converter
Drop BMP files, get tiny AVIFs back — 100% in your browser. No uploads, no accounts, no limits. Batch convert, transparency kept, lossy AVIF at a quality you pick.
100% in-browserNo uploadsFree · no accountBatch up to 20 filesLossy-only AVIFTransparency kept
Windows screenshots, logos and diagrams saved as BMP are pixel-perfect but huge — and many apps, forms and the web only accept modern formats. AVIF is the smallest lossy format in common use: typically 25–35% smaller than PNG or JPG at quality 80, and it keeps transparency — but it is always lossy, never lossless.
Drop BMP files here
or — multiple files welcome
Up to 25 MB per file · up to 20 files per batch · nothing ever uploads
Your BMP is decoded by pure JavaScript built into the page — no decoder download, no waiting.
Loading the AVIF encoder… (about 3.5 MB, once — then it runs entirely in your browser).
Privacy proof — verify it yourself
This page processes your images entirely on your device. Your file data never leaves the device — the only third-party requests are the site’s own analytics, which load at page open and never see your files.
External requests while you use this page: 0 (zero — as it should be)
- Press F12 to open developer tools, then open the Network tab.
- Drop a BMP file above and let it convert.
- Watch the Network tab: no file uploads while it works — the only requests are the site’s analytics, which load at page open. The counter above shows the same number live.
How to convert BMP to AVIF without uploading it
- Drop your BMP files above — or paste one straight from your clipboard. You can add up to 20 at once.
- Pick a quality and width (quality 80 and 800 px are good defaults for the web; Original keeps every pixel). Each BMP becomes one still AVIF. Encoding takes a few seconds for a large photo — the card shows the encode time.
- Download each AVIF, or grab everything as one ZIP. Your originals are untouched and your file data never leaves your device.
Why convert BMP to AVIF at all?
BMP is the format Windows Paint and many scanners save by default because it keeps every pixel — but that makes files huge, and many upload forms, email clients, messaging apps, websites and older programs only accept web formats. AVIF is the smallest lossy format in common use: the same image is typically 25–35% smaller than PNG or JPG at quality 80 with no visible difference, it keeps transparency, and every modern browser displays it. That weight is time your visitor waits — especially on a phone — which is why switching a site's BMPs to AVIF is one of the cheapest PageSpeed wins there is. Keep the BMP as your master copy for editing, and publish the AVIF.
Why is there no lossless mode?
Because the lossless mode in this encoder is broken — and shipping a broken toggle would be worse than having none. When the vendored libavif encoder is asked for lossless output, it produces a monochrome file: a solid red image comes back grey. The lossy path is unaffected — solid red round-trips at max channel difference 1 at quality 100 — so this tool is lossy-only, like the HEIC to AVIF sibling. If you need every pixel exactly, convert to PNG instead, which is lossless. Keep the BMP as your master copy and publish the AVIF.
Honest limitations
- AVIF output is always lossy — there is no lossless mode. The output discards some detail. Quality 80 is visually identical to the original for most photos, but quality 100 is near-lossless, not pixel-perfect. Keep the BMP as your master copy.
- AVIF encoding is slow. The encoder runs single-threaded and searches hard for the smallest packing, so a large photo takes a few seconds — a batch of 20 large photos takes a while. Each card shows its encode time, so you can see the cost instead of wondering why it is taking a moment.
- Transparency is kept, but the output is lossy. A 32-bit BMP's alpha channel survives, including semi-transparent pixels — but a semi-transparent pixel's colour may shift slightly in the lossy encode. Fully transparent pixels keep alpha 0.
- RLE-compressed BMPs are refused — a few old apps saved BMPs with RLE8 or RLE4 compression. This tool refuses them with a clear message; re-save uncompressed (24-bit BMP in Paint) and try again.
- BMP is a still format — a BMP holds exactly one picture, so every output is one still AVIF. Nothing is animated, and nothing is silently dropped.
- BMP carries no EXIF and no orientation — there is no metadata to keep and nothing to rotate. DPI is dropped by the re-encode, so the AVIF carries no DPI value even when the BMP had one.
- 16-bit BMPs are decoded to 8 bits per channel — AVIF only stores 8 bits per channel, so the extra depth is gone. On a standard display the result looks the same, but keep the original if you need the depth.
- Older browsers may not preview AVIF. Every modern browser displays AVIF, but a very old one may show a note on the preview instead of the image — the downloaded .avif file is still valid.
- "Typically 25–35% smaller" is scoped to PNG/JPG comparison only — it compares a lossy AVIF at quality 80 with the same image as PNG or JPG. It is never a guarantee, and it is never claimed against the BMP itself, which is uncompressed and almost always far larger than the AVIF.
- Estimates are estimates — the size shown while converting is a rough model; the real size is shown once conversion finishes.
Frequently asked questions
How can I convert BMP to AVIF without uploading it anywhere?
This converter runs entirely in your browser: it decodes your BMP with a pure JavaScript decoder built into the page and re-encodes it as AVIF with the libavif encoder running on your device. Your file data never leaves the device — the only third-party requests are the site's own analytics, which load at page open and never see your files. Verify it in the Network tab while it works.
Why is my BMP file so large?
BMP is an uncompressed format — every pixel is stored in full, so a BMP is typically much larger than the same image as AVIF, WebP, PNG or JPG. Converting to AVIF shrinks it dramatically, because AVIF predicts neighbouring pixels and packs the result far tighter than raw BMP data. A photo BMP that is 15 MB on disk often becomes an AVIF of a few hundred kilobytes at quality 80, and the tool shows the before and after size honestly for every file.
Is the AVIF output lossless?
No — this tool's AVIF output is always lossy. The quality slider (50 to 100, default 80) trades file size against detail, and at 80 the result is visually identical to the original for almost every photo. Quality 100 is visually near-lossless but not pixel-perfect. There is deliberately no lossless toggle: the vendored encoder's lossless mode produces greyscale files — a colour photo comes back without its colour — so offering it would silently destroy your photos. If you need every pixel exactly, use our BMP to PNG converter instead — PNG is lossless. Keep your BMP as the master copy and use AVIF as the published version.
Why is AVIF encoding slow?
AVIF is the hardest-working lossy format there is — the encoder searches far more ways to pack each block than a JPG or WebP encoder does, and this build runs single-threaded, so a large photo takes a few seconds. A small image converts in well under a second, a typical 800-pixel-wide photo in well under a second, and a 12-megapixel photo in a few seconds. The card shows the encode time for each file, so you can see exactly what it cost. Batch a few files at a time if you are in a hurry.
Does the AVIF keep transparency?
Yes. AVIF stores an alpha channel, so transparency in a 32-bit BMP stays transparent in the AVIF — the preview shows it against a checkerboard so you can see it. That is an advantage over GIF, which flattens transparency onto a background colour, and over JPG, which has no transparency at all. A 32-bit BMP whose alpha byte is 0 everywhere is treated as opaque, because that is an unused alpha channel, not a transparent image.
Will my BMP animate as an AVIF?
No. BMP is a still-image format — a BMP file holds exactly one picture, with no frames and no timing information, so there is nothing to animate. Every output of this tool is one still AVIF per file. If you want a moving AVIF, convert several BMPs here and combine the AVIFs elsewhere, or use a tool that stitches multiple still images into one animated AVIF.
What BMP files can this converter not open?
RLE-compressed BMPs (RLE8 and RLE4) are not supported — most BMPs are uncompressed, but a few old apps saved them compressed, and this tool tells you plainly instead of failing silently. Files that are only named .bmp but are really PNG, JPG or GIF are also refused with a clear message. Corrupt, empty and oversized files are refused the same way.
Can I make the AVIF fit under an upload limit?
Yes — pick a destination preset (website hero aims for under 300 KB, blog image under 150 KB, Discord or forum under 256 KB) and the converter retries with smaller width and lower quality until it fits, or reports the smallest size it could reach. A target is an aim, never a guarantee — the tool reports the size it actually reached on each file.
What happens to bit depth, DPI and metadata?
The decoder reads 1, 4 and 8-bit paletted BMPs, 16-bit 555/565 BMPs, and 24/32-bit BMPs, top-down or bottom-up, and every image is converted to 8 bits per channel, because AVIF only stores 8 bits per channel — the difference is invisible on a standard display, but keep the original if you need the extra depth. BMP carries no EXIF metadata at all, so there is nothing to keep, and DPI is dropped by the re-encode — the AVIF carries no DPI value even when the BMP had one.
Is AVIF really smaller than BMP?
Almost always, by a lot — a BMP stores every pixel uncompressed, so even a lossy AVIF is usually far smaller than the BMP it came from, and a lossy AVIF at quality 80 is typically 25–35% smaller than the same image as PNG or JPG. The tool shows the before and after size honestly for every file, so you can see the saving instead of taking our word for it. If a file ever comes out bigger, the card says so and you can keep the BMP.
Is there a file size or daily limit?
No daily limit, no account. A 25 MB cap per file and 20 files per batch apply, because browsers cannot safely hold larger images in memory. Very large BMPs are also limited to 50 megapixels for the same reason.
How do I verify my files really never upload?
Open developer tools (F12), go to the Network tab, then convert a file. Your file data never leaves your device — the only third-party requests are the site's own analytics, which load at page open and never see your files. The live counter above shows the same number.