Image Compression Ratio Calculator
Upload any image to analyse its compression ratio, bits-per-pixel (BPP), Shannon entropy, and format efficiency score. Understand exactly how well your image is compressed and whether switching to WebP or AVIF would help. Free, no signup, 100% private.
Upload any image to analyse its compression ratio, bits-per-pixel, Shannon entropy, and format efficiency score. All analysis runs locally in your browser — your image never leaves your device.
Why Use Our Image Compression Ratio Calculator?
Four Key Compression Metrics
Our image compression ratio calculator computes compression ratio, bits-per-pixel (BPP), Shannon entropy, and a format efficiency score — giving you a complete picture of how well your image is compressed.
Secure Image Compression Ratio Calculator Online
Your images never leave your device when you use this image compression ratio calculator. 100% client-side processing using the Canvas API ensures complete privacy — safe for confidential assets and sensitive content.
Image Compression Ratio Calculator — No Installation
Calculate image compression ratios directly in your browser. No software downloads, no plugins, no account required. Works on any device with a modern browser.
Instant Analysis with Actionable Insights
Get instant compression analysis with plain-English interpretation of every metric — so you know exactly whether to convert to WebP, AVIF, or keep the current format.
Common Use Cases for Image Compression Ratio Calculator
Web Performance Auditing
Use the image compression ratio calculator to audit images before deploying to production. Identify which images have poor compression ratios and prioritise them for conversion to WebP or AVIF.
PageSpeed & Core Web Vitals
Calculate the compression ratio of your LCP image to understand whether it meets Google's efficiency threshold. Images with BPP above 4 are typically flagged by Lighthouse's 'Efficiently encode images' audit.
CMS & Media Library Optimisation
Analyse images in your WordPress or CMS media library to find poorly compressed files. The efficiency score tells you at a glance which images need re-encoding before they impact page load times.
Format Comparison Research
Compare the compression ratio of the same image saved in JPEG, PNG, WebP, and AVIF to understand the real-world efficiency difference between formats for your specific content type.
Client Reporting & Audits
Generate compression ratio data for client performance audits. The Shannon entropy metric explains why some images compress better than others — useful for educating clients on image optimisation.
Learning Image Compression
Use the image compression ratio calculator as an educational tool to understand how different image formats and content types affect compression efficiency, BPP, and entropy.
Understanding Image Compression Metrics
What is an Image Compression Ratio Calculator?
An image compression ratio calculator is a tool that measures how efficiently an image file is compressed relative to its raw, uncompressed pixel data. The compression ratio tells you how many times smaller the file is than its uncompressed equivalent. A ratio of 10:1 means the file is 10 times smaller than raw pixel data. Our image compression ratio calculator also computes bits-per-pixel (BPP), Shannon entropy, and a format efficiency score— giving you a complete picture of your image's compression quality, entirely in your browser.
How Our Image Compression Ratio Calculator Works
- 1Upload your image: Drag and drop or click to select any image — JPEG, PNG, WebP, GIF, BMP, TIFF, or AVIF. The image compression ratio calculator accepts any browser-decodable format.
- 2Click "Calculate Compression Ratio": The tool draws the image onto an HTML5 canvas, reads the raw pixel data, computes Shannon entropy from the pixel value distribution, and calculates all compression metrics. All processing happens locally in your browser — your image never leaves your device.
- 3Read the results: The tool displays compression ratio, BPP, Shannon entropy, space saved, and a format efficiency score with plain-English interpretation of each metric — so you know exactly what action to take.
What Each Metric Means
- Compression Ratio: Uncompressed size ÷ actual file size. A ratio of 10:1 means the file is 10× smaller than raw pixel data. Higher is better for web delivery.
- Bits Per Pixel (BPP): (File size × 8) ÷ total pixels. Measures how many bits are used to store each pixel. Lower BPP = more compressed. Web images should target ≤ 4 BPP; AVIF/WebP can achieve ≤ 1 BPP at high quality.
- Shannon Entropy:The theoretical minimum bits per pixel needed to represent the image's information content. Images with high entropy (complex textures, photographs) are harder to compress than low-entropy images (flat colors, logos).
- Format Efficiency Score: How close the actual BPP is to the theoretical minimum (Shannon entropy). A score of 100 means near-perfect compression; a score below 40 means significant room for improvement by switching to a more efficient format.
BPP Reference Values by Format
- Uncompressed (BMP/RAW): 24–32 BPP
- PNG (lossless): 8–16 BPP typical
- JPEG (quality 85): 2–4 BPP typical
- WebP (quality 85): 1–3 BPP typical
- AVIF (quality 85): 0.5–2 BPP typical
- Shannon entropy lower bound: 0.1–7.5 BPP depending on image complexity
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Frequently Asked Questions About Image Compression Ratio Calculator
An image compression ratio calculator measures how efficiently an image file is compressed relative to its raw, uncompressed pixel data. It computes the compression ratio (uncompressed ÷ file size), bits-per-pixel (BPP), Shannon entropy, and a format efficiency score. Our free image compression ratio calculator runs entirely in your browser — no uploads required.
For web images, a compression ratio of 5:1 to 20:1 is typical. JPEG at quality 85 achieves roughly 6:1 to 12:1 for photographs. WebP achieves 8:1 to 20:1 at the same visual quality. AVIF can achieve 15:1 to 40:1. Images with ratios below 3:1 are likely under-compressed and should be re-encoded.
Absolutely. Our image compression ratio calculator online processes all images entirely within your browser using the HTML5 Canvas API. Your images are never uploaded to any server, never stored remotely, and never transmitted over the network. This makes it completely safe for confidential assets and sensitive content.
Yes, 100% free. No signup, no subscription, no premium tier, no file size limits, and no watermarks. Our image compression ratio calculator online is free forever.
Shannon entropy measures the information content of an image — specifically, how unpredictable the pixel values are. High entropy (close to 8 bits) means the image has complex, varied content that is hard to compress. Low entropy means the image has repetitive patterns or flat colors that compress very well. The entropy value is the theoretical minimum BPP for lossless compression of that image.
The format efficiency score (0–100) measures how close the actual BPP is to the theoretical minimum (Shannon entropy). A score of 85+ means the format is compressing the image near-optimally. A score below 40 means significant compression gains are possible by switching to a more efficient format like WebP or AVIF.
PNG uses lossless compression, which preserves every pixel exactly. For photographic images with complex color gradients, PNG achieves relatively low compression ratios (2:1 to 4:1) because the pixel data has high entropy. For the same image, JPEG or WebP would achieve much higher ratios by discarding imperceptible detail.
The image compression ratio calculator accepts any browser-decodable image format including JPEG, PNG, WebP, GIF, BMP, TIFF, and AVIF. The tool reads the file size directly and decodes the pixel data via the Canvas API to compute entropy and BPP.
BPP is calculated as (file size in bytes × 8) ÷ total pixels. For example, a 100 KB image with 1 million pixels has a BPP of (100,000 × 8) ÷ 1,000,000 = 0.8 BPP. The uncompressed BPP is 24 for RGB images (3 channels × 8 bits) or 32 for RGBA images (4 channels × 8 bits).