HTTP Header Size Calculator
Estimate total HTTP header bytes.
Keep or share the finished result
Copy or share after running the tool. Saved tools and settings stay in this browser.
What would you like to do next?
Calculate HTTP header size
Large response or request headers can break behind proxies, CDNs and application servers. Paste headers to estimate total bytes, count lines and review per-line size. It is useful for cookie cleanup, debugging 431 errors, API reviews, CDN tuning and performance QA.
Header budget helper
Cookies are a common reason headers grow larger than expected.
Frequently asked questions
What size is too large?
Limits vary, but 8 KB is a useful early warning threshold.
Are bytes exact?
The tool gives a close browser-side byte estimate for pasted text.
Can this prevent every server error?
No. Server, proxy and CDN limits can differ.