This tool uses well-established compression ratio models based on real-world benchmarks. For JPEG, we map quality settings to empirically derived compression ratios (e.g., quality 85 ≈ 7:1 compression). For PNG, complexity input adjusts the estimation. Actual file sizes may vary ±15–25% depending on image content, noise levels, and encoder implementations. Use this as a reliable planning and comparison tool before export.

The four primary factors are: 1) Pixel dimensions — doubling both width and height quadruples raw data; 2) Color depth — 32-bit RGBA uses 33% more raw data than 24-bit RGB; 3) Compression format — JPEG is typically 5–15× smaller than BMP, while PNG is 2–5× smaller; 4) Image complexity — images with large smooth areas compress much better than noisy or highly detailed ones, especially for PNG and lossless formats.

JPEG is best for photographs and complex images where some quality loss is acceptable — it offers the smallest file sizes at good visual quality (quality 75–90). PNG is ideal for graphics with text, logos, screenshots, or images requiring transparency — it's lossless but produces larger files. WebP offers the best of both: lossy WebP is 25–35% smaller than JPEG at equivalent quality, and lossless WebP is typically 26% smaller than PNG. Modern browsers fully support WebP, making it the recommended choice for web use.

Color depth directly determines the amount of raw pixel data. A 24-bit RGB image uses 3 bytes per pixel, while 32-bit RGBA (with alpha/transparency) uses 4 bytes — a 33% increase. 8-bit grayscale uses just 1 byte per pixel. For a 1920×1080 image, the raw difference between 8-bit (≈2MB) and 32-bit (≈8.3MB) is dramatic. However, compression can mitigate these differences — a simple 32-bit PNG with large transparent areas may compress very efficiently.

For web use, quality settings between 75 and 85 offer the best balance of visual quality and file size. Quality 85 typically achieves 6–8:1 compression with minimal visible artifacts. Going above 90 yields diminishing returns — files get much larger with barely perceptible quality improvements. For e-commerce product images, quality 80–85 is standard. For hero banners where quality is critical, quality 85–90 may be warranted. Always test with your specific images, as content type significantly impacts perceived quality.

PNG uses DEFLATE lossless compression, which excels at compressing repeated patterns. A PNG of a simple logo with large flat color areas might compress to 5–10% of its raw size (10–20:1 ratio). However, a PNG of a noisy photograph might only compress to 50–70% of raw size (1.4–2:1 ratio). This is why PNG is recommended for graphics and screenshots, not photographs. Our complexity slider helps account for this variance in estimates.

Several techniques can reduce file size with minimal quality loss: 1) Choose the right format — WebP lossy for photos, PNG for graphics; 2) Use optimal quality settings — JPEG at 80–85 instead of 100; 3) Remove metadata — EXIF data can add 10–50KB; 4) Use modern encoders — tools like MozJPEG or libvips produce smaller files than standard encoders; 5) Consider lazy loading & responsive images — serve appropriately sized images instead of oversized ones; 6) Use SVG for vector graphics when possible.

Lossless compression (PNG, WebP lossless, GIF) preserves every pixel exactly — the decompressed image is identical to the original. This is essential for text, logos, and medical imaging. Lossy compression (JPEG, WebP lossy) discards some visual information that the human eye is less sensitive to, achieving much smaller file sizes at the cost of some fidelity. Modern lossy codecs are very sophisticated — at quality 85+, most viewers cannot tell the difference from the original, while file sizes are 5–15× smaller.