Image File Size Calculator
Estimate image file size from dimensions, format, and quality, or upload a real image for browser-based JPG, WebP, and PNG encoding measurements.
Estimate bytes with useful context
Raw memory calculation
See width × height × four-channel RGBA memory before compression.
Real browser encoding
Upload an image to measure an actual Canvas-encoded blob at selected dimensions and quality.
JPG, WebP, and PNG
Compare photographic lossy formats with lossless PNG while recognizing that content complexity changes results.
What controls image file size?
| Setting | Result | Best use |
|---|---|---|
| Pixel dimensions | More pixels usually require more bytes | Resize oversized web images |
| Format | Codecs compress different content differently | JPG/WebP for photos, PNG for lossless graphics |
| Quality setting | Lower lossy quality reduces bytes | Balance artifacts against performance |
| Image complexity | Noise and fine texture compress poorly | Test with the actual source image |
How it works
- 1
Enter dimensions
Type output width and height or upload a source image.
- 2
Select encoding
Choose JPG, WebP, or PNG and adjust lossy quality.
- 3
Compare estimates
Review raw memory and the actual browser-encoded result.
Why image file size cannot be predicted exactly
Uncompressed RGBA memory is straightforward: width × height × 4 bytes. Compressed file size is content-dependent. Flat colors and smooth backgrounds compress differently from noise, foliage, hair, text, or detailed textures.
Quality scales are encoder-specific and PNG ignores a lossy quality slider. Browser Canvas estimates are useful but may differ from Photoshop, command-line encoders, CMS optimization, or CDN processing. Always measure the final production asset.
Frequently asked questions
How do I calculate uncompressed image size?
For standard RGBA memory, multiply width by height by four bytes.
Can compressed file size be calculated exactly from dimensions?
No. It depends on image content, format, encoder, metadata, and quality settings.
Why does PNG quality not change like JPG?
PNG is normally lossless; file size depends on pixel patterns and compression implementation rather than a lossy quality target.
Is the uploaded image sent to a server?
No. The estimate uses browser Canvas locally.
Image File Size Calculator last reviewed: Aug 2, 2026.