← ToolBox / Base64 编码长度

🔤 Base64 Encoded Length

Measure the encoded length and byte size of inputs with quick local calculation.

原始字节数

含填充 1/0

换行字符数(0不换)

Base64 每 3 字节编码为 4 字符
字符数 = ⌈n/3⌉ × 4（含填充）；余 1 字节补 2 个 =、余 2 字节补 1 个 =

base64 不可缩短，仅作长度估算。

📚 深度解析：Base64 编码长度

示例：100 KB 文件

100×1024 字节 → ⌈100×1024/3⌉×4 ≈ 136,708 字符，约 133 KB（膨胀 1/3）。

Item	Formula / Rule	Source / Standard
Encoded length	L = 4 × ⌈n / 3⌉ where n is the input byte count	RFC 4648 §4 Base 64 Encoding
Padding	Padding = (3 − n mod 3) mod 3 "=" characters, rounding up to a multiple of four	RFC 4648 §3.2 Padding of Encoded Data
Size overhead	Overhead = 4/3 − 1 ≈ 33.3%, since every three bytes become four characters	RFC 4648 §4, 6-bit group mapping