JWT Token Size Calculator
Estimate JWT token sizes before implementation. Compare algorithms, check size limits for cookies, headers, and URLs, and optimize your token payload for better performance.
Fast symmetric signing with 256-bit hash
Enter a valid JSON object with your JWT claims (e.g., sub, iat, exp, custom claims)
Related Calculators
You might also find these calculators useful
Calculate JWT Token Size Before Implementation
JSON Web Tokens (JWT) are the industry standard for secure authentication and authorization. However, token size impacts performance, storage limits, and network overhead. Our JWT Token Size Calculator helps you estimate token sizes, compare algorithms, and optimize your payload before writing any code.
Why Calculate JWT Token Size?
Avoid Cookie Size Limits
Browsers limit cookies to 4KB. Large JWTs stored in cookies can cause silent failures and authentication issues.
Optimize Network Performance
JWTs are sent with every authenticated request. Smaller tokens mean faster page loads and lower bandwidth costs.
Choose the Right Algorithm
RSA signatures are much larger than ECDSA or HMAC. Understanding the tradeoffs helps you choose wisely.
Plan URL-Based Authentication
Passing JWTs in URL parameters has strict length limits (~2000 characters). Calculate before implementing.
How to Use This Calculator
Frequently Asked Questions
Base64 encoding converts binary data to ASCII text using 64 characters. Every 3 bytes of input become 4 characters of output, resulting in approximately 33% size increase.