BMP to PNG Converter — Lossless Compression, 70% Smaller

Convert BMP to PNG Online — Lossless, Free, No Uploads

BMP and PNG are both lossless image formats, which is why converting between them is one of the rare cases where you get everything and give up nothing. BMP stores every pixel as raw data with no compression at all — which is why a 1920×1080 image weighs in at roughly 6 MB regardless of content. PNG applies DEFLATE compression, the same algorithm used inside ZIP files, and typically shrinks that same image to 1–3 MB without changing a single pixel.

There is no quality trade-off here. The two formats store the same pixel data — one in a fat uncompressed wrapper, the other in a compressed one. If the source BMP is 24-bit RGB, the PNG will be 24-bit RGB. If the BMP had a palette, the PNG can keep a palette. The only visible difference is the file extension and the disk space it takes up.

This tool runs entirely in your browser using the HTML canvas element. Your BMPs are read from your disk, decoded in memory, and saved back as PNG without ever touching a server. That matters because the files you are converting are often screenshots, CAD exports, or documentation images you would rather not upload to a stranger's machine.

Why BMP Files Are So Big — and Why PNG Fixes It

BMP stores pixel data at a fixed cost per pixel. A 24-bit BMP uses 3 bytes per pixel, plus a small header. Multiply by the pixel count and you have the file size before any metadata. A 4K screenshot at 3840×2160 is 8.3 million pixels, so the BMP lands around 24 MB. PNG takes those same 8.3 million pixel values, runs them through DEFLATE compression, and typically produces a file in the 2–4 MB range — sometimes smaller for flat-color graphics.

How Much Smaller Is PNG?

Real numbers from common cases:

• A 6 MB BMP screenshot → a 1–2 MB PNG. Text and UI stay razor sharp because PNG is lossless.
• A 24 MB BMP 4K screenshot → a 3–5 MB PNG. Clean lines, no compression artifacts.
• A 20 MB BMP photo → a 12–16 MB PNG. Less dramatic savings, since photographs have noisy data that compresses poorly without loss.
• A 3 MB BMP flat-color graphic → a 100–300 KB PNG. This is where PNG shines brightest — flat colors and limited palettes compress extremely efficiently.

When PNG Is the Right Choice — and When It Isn't

PNG is the right output for screenshots, UI mockups, technical diagrams, icons, logos, and anything that needs pixel-perfect fidelity. It is also the right choice when the image might be edited further — lossless is a better starting point than lossy. It is the wrong choice for two cases: when file size matters more than fidelity (use JPG for photos), or when the modern web is the target and you want the smallest possible files (use WebP).

Where BMP Files Come From

The main sources of BMP files today:

• Microsoft Paint, which historically defaulted to BMP.
• Windows Snipping Tool in older versions.
• CAD and technical drawing software that exports raw bitmaps.
• Legacy Windows applications that write images to disk.
• Industrial imaging and microscopy software that needs exact pixel values.

How the Conversion Actually Works

When you click Convert, each BMP is loaded into an HTML canvas element. The canvas reads the raw pixel data directly, then exports it as a PNG using the browser's built-in encoder. The encoder follows the W3C PNG specification (ISO/IEC 15948) and writes DEFLATE-compressed data, which is why the output is lossless. A typical 6 MB BMP converts in under a second on a modern laptop.

Why This Beats Uploading to an Online Converter

Every server-based converter — CloudConvert, Convertio, Zamzar, and others — makes you upload the BMP before it can start. On a 24 MB file over a home connection, that is 30 seconds to a few minutes of dead time before any conversion happens. This tool reads the file from disk and starts converting immediately, so the wall-clock time is under a second per file regardless of size. The privacy angle is a bonus: nothing leaves your device.