JWT Token Size, Base64URL Overhead & TTL Calculator

Calculate JWT token byte size (HS256, RS256, ES256, EdDSA), Base64URL overhead, 4 KB browser cookie and 8 KB Nginx header limits, and monthly bandwidth.

Input Parameters

Try Example:

Calculation Results

4 KB Browser Cookie Limit Utilization (908 / 4096 Bytes)22.00%

JWS Signing Algorithm: RS256
Raw Header JSON Size: 46 Bytes
Encoded Header Segment (Base64URL): 62 Bytes
Effective Payload JSON Size: 376 Bytes
Encoded Payload Segment (Base64URL): 502 Bytes
Raw Binary Signature Size: 256 Bytes
Encoded Signature Segment (Base64URL): 342 Bytes
Total JWT Token Size: 908 Bytes
HTTP Authorization Header Size: 932 Bytes
Base64URL Encoding Overhead: 33.92 %
Browser Cookie 4 KB Limit Status: Aman untuk Browser Cookie (< 4 KB)
Nginx 8 KB Header Buffer Status: Aman untuk Default Header Proxy Nginx/Cloudflare (< 8 KB)
Token Expiration Duration (TTL): 1 Hours
Daily Header Bandwidth Overhead: 88.88 MiB/Day
Monthly Header Bandwidth Overhead (30d): 2.604 GiB/Month

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JWT Token Footprint Comparison by Signing Algorithm

JWS Signing Algorithm	Raw Signature (Bytes)	Base64URL Signature (Chars)	Total JWT Size (Bytes)
HS256	32 Bytes	43 Bytes	583 Bytes
ES256	64 Bytes	86 Bytes	652 Bytes
EdDSA	64 Bytes	86 Bytes	652 Bytes
HS512	64 Bytes	86 Bytes	626 Bytes
RS256	256 Bytes	342 Bytes	908 Bytes
RS512	512 Bytes	683 Bytes	1,223 Bytes

JWT Token Segment & Header Anatomy

Authorization: Bearer <header:62B>.<payload:502B>.<signature:342B>
Header JSON (46B)  -> {"alg":"RS256","typ":"JWT"},"kid":"key-2026"
Payload JSON (376B) -> {"sub":"usr_9281","iat":1762473600,"exp":1762477200,"claims":4}
Signature (256B raw -> 342B Base64URL) | Total HTTP Header: 932 Bytes

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How to Use This Tool

Select the JWT signing algorithm (HS256, RS256, ES256, EdDSA, HS512, or RS512) and enter the base JSON payload size along with the number of custom claims.
Enter the token Time-To-Live (TTL in minutes) and the average number of daily API requests.
Inspect the total JWT byte size, 4 KB browser cookie and 8 KB Nginx header compliance status, monthly bandwidth overhead, and the algorithm comparison table.

Worked Example: Standard API Gateway Microservice (RS256, 280B Payload)

Worked example: An RS256 token with a 280-byte base payload + 4 custom claims (376B JSON total) produces a 62B header, 502B Base64URL payload, and 342B signature = 908 bytes total JWT (932 bytes with HTTP Authorization header).

Example Input

Cryptographic Signing Algorithm (JWS): RS256 (RSA 2048-bit Signature — 256 Raw Bytes)
Base Payload JSON Size (Bytes): 280 Byte
Additional Custom Claims Count: 4
Token Time-To-Live / TTL (Minutes): 60 Menit
Average API Requests per Day: 100,000

Calculated Output

JWS Signing Algorithm: RS256
Raw Header JSON Size: 46 Bytes
Encoded Header Segment (Base64URL): 62 Bytes
Effective Payload JSON Size: 376 Bytes
Encoded Payload Segment (Base64URL): 502 Bytes
Raw Binary Signature Size: 256 Bytes
Encoded Signature Segment (Base64URL): 342 Bytes
Total JWT Token Size: 908 Bytes
HTTP Authorization Header Size: 932 Bytes
Base64URL Encoding Overhead: 33.92 %
Browser Cookie 4 KB Limit Status: Aman untuk Browser Cookie (< 4 KB)
Nginx 8 KB Header Buffer Status: Aman untuk Default Header Proxy Nginx/Cloudflare (< 8 KB)
Token Expiration Duration (TTL): 1 Hours
Daily Header Bandwidth Overhead: 88.88 MiB/Day
Monthly Header Bandwidth Overhead (30d): 2.604 GiB/Month
JWT Token Segment & Header Anatomy: Authorization: Bearer <header:62B>.<payload:502B>.<signature:342B> Header JSON (46B) -> {"alg":"RS256","typ":"JWT"},"kid":"key-2026" Payload JSON (376B) -> {"sub":"usr_9281","iat":1762473600,"exp":1762477200,"claims":4} Signature (256B raw -> 342B Base64URL) | Total HTTP Header: 932 Bytes

JWT Token Footprint Comparison by Signing Algorithm

JWS Signing Algorithm	Raw Signature (Bytes)	Base64URL Signature (Chars)	Total JWT Size (Bytes)
HS256	32 Bytes	43 Bytes	583 Bytes
ES256	64 Bytes	86 Bytes	652 Bytes
EdDSA	64 Bytes	86 Bytes	652 Bytes
HS512	64 Bytes	86 Bytes	626 Bytes
RS256	256 Bytes	342 Bytes	908 Bytes
RS512	512 Bytes	683 Bytes	1,223 Bytes

Core Concept & Engineering Notes

JSON Web Tokens (JWT), standardized under IETF RFC 7519, provide a compact, URL-safe format for transmitting authenticated identity claims and authorization metadata across microservices, API gateways, and client applications. A cryptographically signed JWT (JWS — RFC 7515) comprises three dot-separated segments: the JOSE Header declaring the signing algorithm and key identifier, the Payload containing JSON claims (such as sub, iat, exp, and user roles), and the binary Signature verifying integrity. Each segment is serialized using Base64URL encoding (RFC 4648). Because Base64URL maps every 3 bytes of raw binary input (24 bits) into 4 ASCII characters (6 bits per character), both the JSON payload and raw cryptographic signature incur an inherent ~33.33% size expansion. Furthermore, the chosen signing algorithm dramatically impacts total token footprint: symmetric HMAC-SHA256 (HS256) and modern elliptic-curve algorithms like ECDSA P-256 (ES256) or EdDSA (Ed25519) produce compact signatures (32 to 64 raw bytes, encoding to 43–86 characters), whereas 2048-bit RSA (RS256) generates a 256-byte signature (342 Base64URL characters). Because JWTs are transmitted on every HTTP request via the Authorization: Bearer header or stored in browser cookies, token bloat creates tangible infrastructure bottlenecks. Web browsers enforce a strict 4,096-byte (4 KB) ceiling per cookie, and reverse proxies such as Nginx default to an 8 KB buffer limit per individual HTTP header (large_client_header_buffers). Beyond triggering HTTP 431 Request Header Fields Too Large rejections or silent browser cookie eviction, oversized tokens compound bandwidth overhead across high-throughput API gateways. Embedding verbose permission arrays, full user profiles, or organizational hierarchies directly inside stateless JWT payloads forces clients to upload kilobytes of redundant metadata on every API call. Following OAuth 2.0 and OpenID Connect best practices—restricting JWT payloads to essential claims (sub, iss, aud, exp, jti) and migrating asymmetric signing from RS256 to ES256 or EdDSA—slashes signature overhead by 75% while preserving full cryptographic non-repudiation.

How It Was Calculated (Formulas & Steps)

Mathematical Formulas

Base64URL Character Length = ceil((Raw_Byte_Length × 4) ÷ 3)
Total JWT Token Size = Len(Header_B64) + 1 + Len(Payload_B64) + 1 + Len(Signature_B64)
HTTP Authorization Header Size = Total_JWT_Bytes + 24 bytes ('Authorization: Bearer \r\n')

Step-by-Step Calculation

Header JSON = 46 byte → Base64URL: ⌈46 × 4 / 3⌉ = 62 karakter.
Payload JSON efektif = 280 + (4 klaim × 24B) = 376 byte → Base64URL: ⌈376 × 4 / 3⌉ = 502 karakter.
Signature RS256 = 256 byte biner → Base64URL: ⌈256 × 4 / 3⌉ = 342 karakter.
Total Token JWT = 62 + 1 + 502 + 1 + 342 = 908 byte (Header HTTP Authorization: 932 byte).
Trafik Bulanan (100,000 req/hari × 30 hari) = 2.604 GiB/bulan khusus header autentikasi.

Frequently Asked Questions (FAQ)

Why does switching from RS256 to ES256 or EdDSA significantly reduce JWT token size?

A 2048-bit RSA key produces a 256-byte raw signature (342 Base64URL characters), whereas elliptic-curve ES256 or EdDSA achieves equivalent asymmetric security with a 64-byte signature (86 characters), saving 256 bytes on every HTTP request.

What happens if a JWT exceeds 4,096 bytes when stored in a browser cookie?

Per RFC 6265, browsers silently drop cookies exceeding the 4 KB storage limit, causing authentication flows to fail intermittently when users accumulate many permission claims.

Why does Nginx return HTTP 400 Bad Request or 431 Request Header Fields Too Large?

By default, Nginx configures large_client_header_buffers to 4×8k. If an Authorization or Cookie header carrying a bloated JWT exceeds 8 KB, Nginx rejects the request before proxying to the upstream server.

What is the recommended TTL (expiration time) for a stateless JWT Access Token?

Because stateless JWTs cannot be revoked before expiration without maintaining a server-side denylist, access tokens should use a short TTL of 5 to 15 minutes paired with a revocable Refresh Token.

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References & Notes

Last updated: 2026-11-07Technically Verified · Industry Standard

Note: Results above are mathematical estimates based on standard formulas. Always verify against official vendor documentation and site conditions before production deployment.