HTTP Header Size Calculator
Calculate HTTP header overhead across a page load and the saving from compression.
About HTTP Header Size Calculator
Headers are sent on every request, so a large cookie multiplies across the whole page load and consumes scarce uplink bandwidth. HTTP/2 header compression removes most of the repetition. Cookies on static asset domains are pure waste, which is why serving assets from a cookieless domain was standard practice before HTTP/2.
Formula
HTTP Header Size
Header overhead = requests × (request + cookie + response header bytes)
- HPACK
- HTTP/2 header compression, which removes most repeated header bytes
- cookie overhead
- Cookies are sent on every request to the origin
Worked example
With the default values below, HTTP Header Size Calculator returns Total Header Overhead of 130.469. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Requests per page loadminimum 0
- 80
- Average request header sizeminimum 0 bytes
- 750 bytes
- Average response header sizeminimum 0 bytes
- 520 bytes
- Cookie size sent per requestminimum 0 bytes
- 400 bytes
- Saving from HTTP/2 header compressionaccepts 0–100 %
- 80 %
Results
- Total Header Overhead
- 130.469 KB
- Header Overhead After Compression
- 26.094 KB
- Overhead From Cookies Alone
- 31.250 KB
- Uplink Header Traffic
- 89.844 KB
- Saving From Compression
- 104.375 KB
Step by step
- 1Values used
- 2HTTP Header Size
- 3Total Header Overhead= 130.469 KB
- 4Header Overhead After Compression= 26.094 KB
- 5Overhead From Cookies Alone= 31.250 KB
- 6Uplink Header Traffic= 89.844 KB
- 7Saving From Compression= 104.375 KB
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is HTTP Header Size calculated?
Header overhead = requests × (request + cookie + response header bytes) Headers are sent on every request, so a large cookie multiplies across the whole page load and consumes scarce uplink bandwidth. HTTP/2 header compression removes most of the repetition.
Why does HTTP Header Size matter?
Cookies on static asset domains are pure waste, which is why serving assets from a cookieless domain was standard practice before HTTP/2.
What values do I need to enter?
This calculator takes 5 inputs: Requests per page load, Average request header size, Average response header size, Cookie size sent per request, Saving from HTTP/2 header compression. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.