How to Use Image File Size Calculator
The Image File Size Calculator estimates how large an image file will be before you create or export it, helping you optimise assets for web performance and storage.
- Enter Width and Height — Input the image dimensions in pixels. The Image File Size Calculator uses these to determine total pixel count.
- Select Bit Depth — Choose the colour depth that matches your image type: 24-bit for standard RGB photos, 32-bit for images with transparency, or 8-bit for grayscale.
- Choose a Format — Select the target image format (JPG, PNG, WebP, AVIF, BMP, GIF, or TIFF). The Image File Size Calculator applies the typical compression characteristics of each format.
- Adjust Quality (lossy formats) — For JPG, WebP, and AVIF, drag the quality slider to reflect your export settings. Lower quality reduces file size at the cost of visual fidelity.
- Read the Results — The Image File Size Calculator displays the raw uncompressed size and the estimated compressed file size side by side.
Formula & Theory — Image File Size Calculator
The Image File Size Calculator is built on the fundamental pixel-data formula:
Uncompressed Size (bytes) = Width × Height × Bit Depth ÷ 8
Estimated File Size = Uncompressed Size × Compression Ratio × Quality Factor
| Symbol | Meaning |
|---|---|
| Width | Image width in pixels |
| Height | Image height in pixels |
| Bit Depth | Bits used to represent one pixel (e.g., 24 for RGB) |
| Compression Ratio | Format-specific factor (e.g., ~0.10 for JPG at default quality) |
| Quality Factor | Multiplier for lossy formats derived from the 0–100 quality scale |
Typical Compression Ratios by Format
| Format | Typical Ratio vs. Uncompressed |
|---|---|
| BMP | ~1.0 (no compression) |
| TIFF | ~0.9 (lossless, minimal) |
| PNG | ~0.5 (lossless) |
| GIF | ~0.35 (lossless, 256 colours) |
| JPG (Q80) | ~0.10 |
| WebP (Q80) | ~0.07 |
| AVIF (Q80) | ~0.05 |
The Image File Size Calculator adjusts these ratios dynamically based on your quality slider value, giving you a realistic estimate for any export setting.
Use Cases for Image File Size Calculator
The Image File Size Calculator is valuable in many professional workflows:
- Web performance optimisation — Predict whether a hero image or product photo will exceed your page-weight budget before exporting, saving time in iterative quality adjustments.
- Bandwidth and CDN cost planning — Estimate monthly data transfer costs by knowing the average size of images served at different resolutions and formats.
- Storage capacity planning — Calculate how many images of a given resolution and format will fit on a server volume or cloud storage bucket.
- Format comparison — Use the Image File Size Calculator to compare JPG, WebP, and AVIF at the same quality setting and choose the most efficient format for your use case.
- Upload size validation — Check whether an image will fall within the maximum file size enforced by a CMS, e-commerce platform, or social network before the upload fails.
- Print media — Estimate the file size of high-resolution TIFF or BMP exports used in print production workflows.
The Image File Size Calculator gives designers, developers, and digital marketers the data they need to make informed decisions about image format, resolution, and quality settings.