Digital Signature Size Calculator
Compare signature and public-key sizes across RSA, ECDSA, Ed25519 and ML-DSA in raw, DER or Base64 encoding.
Inputs
Encoded Signature Size
88bytes
Raw Signature Size
64bytes
Public Key Size
91bytes
Security Strength
128bits
Total Storage
83.92MiB
Assessment
Classically strong at 128 bits, but Shor-breakable
Step by step
Values used
Signature algorithm = ECDSA P-256; Wire encoding = Base64 / JWS; Signatures stored or transmitted = 1,000,000 signatures
Digital Signature Size
an ECDSA signature is 2 × ⌈field ÷ 8⌉ raw bytes, an RSA signature equals the modulus in bytes, and Base64 inflates any of them to 4 × ⌈bytes ÷ 3⌉.
Encoded Signature Size
= 88 bytes
Raw Signature Size
= 64 bytes
Public Key Size
= 91 bytes
Security Strength
= 128 bits
Total Storage
= 83.92 MiB
Assessment
= Classically strong at 128 bits, but Shor-breakable
How it works
ECDSA and Ed25519 signatures are two field elements, so P-256 gives 64 raw bytes against RSA-2048's 256. ML-DSA-65 trades size for quantum resistance: a 3,309-byte signature and a 1,952-byte public key, roughly 50× an Ed25519 signature. Signature size lands directly in JWT headers, certificate chains, blockchain records and firmware images — the jump to post-quantum signatures is the main reason those formats need size headroom now.
Formula
Digital Signature Size
an ECDSA signature is 2 × ⌈field ÷ 8⌉ raw bytes, an RSA signature equals the modulus in bytes, and Base64 inflates any of them to 4 × ⌈bytes ÷ 3⌉.
- raw
- The bare signature value
- DER
- ASN.1 SEQUENCE of the two ECDSA integers, ~8 bytes of tags and lengths
- Base64
- JWS and PEM encoding, 33% larger
Frequently Asked Questions
How is Digital Signature Size calculated?
an ECDSA signature is 2 × ⌈field ÷ 8⌉ raw bytes, an RSA signature equals the modulus in bytes, and Base64 inflates any of them to 4 × ⌈bytes ÷ 3⌉. ECDSA and Ed25519 signatures are two field elements, so P-256 gives 64 raw bytes against RSA-2048's 256. ML-DSA-65 trades size for quantum resistance: a 3,309-byte signature and a 1,952-byte public key, roughly 50× an Ed25519 signature.
Why does Digital Signature Size matter?
Signature size lands directly in JWT headers, certificate chains, blockchain records and firmware images — the jump to post-quantum signatures is the main reason those formats need size headroom now.
What values do I need to enter?
This calculator takes 3 inputs: Signature algorithm, Wire encoding, Signatures stored or transmitted. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Why do ECDSA signatures vary by a byte or two in DER?
DER encodes r and s as signed integers, so a leading zero is prepended when the high bit is set and stripped when the value is short. A P-256 DER signature is therefore usually 70–72 bytes, which is why parsers must not assume a fixed length.