How to use this calculator
- Enter or choose file sizes in.
- Enter or choose original size.
- Enter or choose compressed size.
- Enter or choose image loads per month.
- Enter or choose bandwidth price per GB.
- The transfer saved per month updates as you type. Use Copy result or Share to keep it.
Method
Bytes saved = (Original − Compressed) × 1,000 (or 1,024); GB saved = Bytes saved × Loads ÷ 10⁹; Time saved = Bytes saved × 8 ÷ (Mbps × 10⁶)
- Loads
- downloads of the image per month
- Mbps
- connection speed in megabits per second (8 bits per byte)
Worked example
- Saved per load: 500 − 150 = 350 kB = 350,000 bytes (70%).
- Per month: 350,000 × 1,000,000 = 3.5 × 10¹¹ bytes = 350 GB; × 0.08 = 28.
- Time: 350,000 × 8 = 2.8 million bits ÷ 10 Mbps = 0.28 s = 280 ms.
Cutting a 500 kB image to 150 kB saves 350 GB a month at a million loads, and about 280 ms per load on a 10 Mbps connection.
What the result means
Bandwidth savings matter at scale, but the load-time saving usually matters more: smaller hero images improve Largest Contentful Paint, which affects user experience and search visibility.
Assumptions and limits
- Every load transfers the whole file.
- Time saved assumes the connection is the bottleneck, ignoring latency.
- HTTP compression, caching and responsive image sizes mean real savings vary by visitor.
Questions
Why are bits and bytes mixed here?
File sizes are in bytes, but connection speeds are quoted in bits per second. One byte is 8 bits, so a 10 Mbps line moves 1.25 MB per second at best.
Which formats compress best?
For photos, AVIF and WebP are usually much smaller than JPEG at similar visual quality; measure with your own images.