You saved a screenshot in Microsoft Paint and the file is 5.9 megabytes. You opened the same image in Chrome and saved it as JPEG and it is 320 kilobytes. Same picture, same monitor resolution — nearly 19 times smaller. This is not a bug or an error. It is the fundamental difference between how BMP and JPEG store image data, and once you understand it, you will never look at file formats the same way.
The BMP format makes zero decisions about your image. It stores exactly what is on screen — every single pixel, in full color, with no compression, no approximation, no shortcuts. This makes it perfectly faithful and perfectly enormous. JPEG, by contrast, is an intelligent compression algorithm that identifies patterns, throws away information the human eye cannot perceive, and stores only the mathematical essence of the image.
This article explains the exact technical reason BMP files are so large, how TIFF differs, and when you should convert each format to JPG or PNG.
What Is a BMP File? The Technical Reality
BMP stands for Bitmap. The name is literal — it is a map of bits (pixels) stored one by one. The format was created by Microsoft in the early 1980s and became the native image format for Windows. Every version of Windows, from Windows 1.0 to Windows 11, can read and write BMP files without any additional software.
The BMP Size Formula — Exact Math
The size of an uncompressed 24-bit BMP file is almost perfectly predictable with this formula:
For a 1920×1080 screenshot:
1920 × 1080 × 3 = 6,220,800 bytes = 5.93 MB
For a 4K screenshot (3840×2160):
3840 × 2160 × 3 = 24,883,200 bytes = 23.7 MB
The three bytes per pixel represent one byte each for the Red, Green, and Blue channel of every single pixel. There is no consideration for whether adjacent pixels are the same color. Even if your screenshot is entirely white — all 2 million pixels the same color — a BMP file stores all 2 million pixels individually. A PNG would represent that white area in a handful of bytes using run-length encoding.
Why Windows Still Uses BMP
Despite its inefficiency, BMP persists because of its simplicity and universal compatibility. Any Windows application from any era can read BMP without any codec or library. The Windows clipboard stores image data internally as a BMP-like format. Microsoft Paint defaults to BMP not because it is optimal, but because it is the most universally readable format in the Windows ecosystem. For screenshots and diagrams passed between legacy Windows applications, BMP's total compatibility outweighs its size disadvantage.
What Is a TIFF File and Why Can It Be Even Larger?
TIFF (Tagged Image File Format) was created in 1986 by Aldus Corporation as a flexible, professional image format. Unlike BMP, TIFF is actually a container format — it can store image data in multiple ways:
| TIFF Variant | Compression | Typical Size (1920×1080) | Common Source |
|---|---|---|---|
| TIFF Uncompressed (8-bit) | None | ~6 MB | Basic scanners |
| TIFF Uncompressed (16-bit) | None | ~12 MB | High-end scanners, cameras |
| TIFF LZW Compressed | Lossless LZW | ~3–6 MB | Document management systems |
| TIFF ZIP Compressed | Lossless Deflate | ~2–5 MB | Professional photography software |
| TIFF CMYK (print) | None or LZW | ~8–16 MB | Print production, InDesign |
Why TIFF Is Used in Professional Settings
Unlike BMP, TIFF was designed with professional requirements in mind. It supports multiple color modes (RGB, CMYK, grayscale, Lab, even YCbCr), multiple bit depths (8-bit, 16-bit, 32-bit per channel), embedded color profiles (ICC profiles for color-managed workflows), extensive metadata (EXIF camera data, IPTC copyright info, XMP custom fields), multi-page files (a single TIFF can contain an entire multi-page scanned document), and transparency (alpha channel support). These features make TIFF indispensable in medical imaging, print production, scientific research, and archival photography.
Why Both Are Impractical for Everyday Sharing
The practical problem is simple: you cannot email a 6 MB BMP screenshot when you could share the same image as a 350 KB JPEG. You cannot upload a 16 MB TIFF scan to a website that has a 2 MB upload limit. You cannot post a 23 MB BMP to social media when Instagram downsizes everything anyway. In all of these scenarios, converting to convert bmp tiff to jpeg online produces a file that is dramatically smaller with virtually no visible quality loss for photographic content.
Size Comparison: The Same Image, Four Formats
To make the scale tangible, here is what happens when a typical 1920×1080 photograph is saved in each format:
| Format | File Size | Quality | Compression Type | Email Practical? |
|---|---|---|---|---|
| BMP (24-bit) | 5.9 MB | Lossless | None | No |
| TIFF (uncompressed, 16-bit) | 12–16 MB | Lossless | None | No |
| PNG | 1.2–2 MB | Lossless | Deflate | Sometimes |
| JPEG (85% quality) | 300–450 KB | Excellent | Lossy DCT | Yes |
| WebP (lossy) | 200–320 KB | Excellent | Lossy VP8 | Yes |
When to Keep BMP or TIFF — Do Not Always Convert
There are legitimate reasons to keep files in BMP or TIFF format:
- Windows application integration: Some legacy business software only accepts BMP input. Keep BMP for these workflows.
- Print production masters: TIFF CMYK files are the industry standard for commercial printing. Never convert these to JPEG — you lose the CMYK color mode and introduce lossy artifacts into print artwork.
- Medical and scientific archival: TIFF is used in pathology, radiology, and microscopy because lossless fidelity is required. Convert only for reporting, not for archival.
- Photography editing masters: Keep TIFF versions of edited photos. Export JPEG for web galleries and client delivery.
- Multi-page document archival: A 50-page TIFF scan of a legal document is the archival master. Keep it. Share individual pages as JPEG for review.
Best BMP to JPG Converter: Convert Legacy Windows Images to JPEG Free (2026) — top tools compared with quality settings guide
BMP vs TIFF vs JPG vs PNG: Which Legacy Format Should You Convert From? — full format comparison matrix
