Vad Är Base64-kodning? En Komplett Förklaring
Quick Answer
Base64-kodning konverterar binär data till text med 64 utskrivbara tecken (A-Z, a-z, 0-9, +, /). Varje 3 bytes input blir 4 Base64-tecken. Base64 är reversibelt (inte kryptering) och ökar datastorlek ~33%. Använd vår gratis Base64 Encoder och Decoder.
Introduction
Base64 är ett binärt-till-text-kodningsschema som konverterar binär data till en ASCII-sträng med 64 utskrivbara tecken. Det är definierat av RFC 4648 och används ofta för att koda data som måste överföras via text-medier —email-bilagor (MIME), Data URLs, JWT-token-delar och JSON-payloads med binär data. Base64 är kodning, inte kryptering —det är fullt reversibelt och kräver ingen nyckel.
Step by Step
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Understand the character set
Base64 uses 64 characters: A-Z (26), a-z (26), 0-9 (10), + and / (2). The = character is used for padding when the input length is not a multiple of 3. The URL-safe variant replaces + with - and / with _ and omits padding.
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Learn how encoding works
Base64 processes input in 3-byte (24-bit) blocks. Each 24-bit block is split into four 6-bit groups. Each 6-bit value (0-63) maps to one of the 64 characters. If the input is not a multiple of 3, padding (=) is added: 1 byte input → 2 Base64 chars + ==, 2 bytes → 3 chars + =.
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Understand the size overhead
Base64 increases data size by approximately 33% — every 3 bytes becomes 4 characters. A 1 MB file becomes ~1.33 MB when Base64-encoded. This overhead is the trade-off for text-only compatibility.
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Distinguish encoding from encryption
Base64 is encoding, not encryption. It is reversible without a key — anyone can decode it. Base64 provides no confidentiality; it only converts binary to text for transport. Never use Base64 to store passwords or secrets.
Examples
Encode text
Input: Hello, World!
Output: SGVsbG8sIFdvcmxkIQ==
Encode binary data (shown as hex)
Input: Bytes: 0x00 0x01 0x02
Output: AAEC
URL-safe Base64 (JWT style)
Input: Standard: SGVsbG8= → URL-safe: SGVsbG8 (no padding, - and _ for + and /)
Output: Used in JWT tokens and URL parameters
Common Problems
- Treating Base64 as encryption —Base64 is reversible without a key. Anyone can decode it. Never use it to protect sensitive data.
- Non-ASCII characters —naive btoa() throws on Unicode. Use TextEncoder + btoa(unescape(encodeURIComponent(text))) or a UTF-8-aware tool.
- Padding removal —the = padding is part of the encoding. Removing it breaks decoding (though some decoders can reconstruct it).
- Size overhead —Base64 adds ~33% to data size. For large files, this is significant; consider whether encoding is necessary.
Tips
- Use Base64 for Data URLs to embed small images in HTML/CSS without a separate HTTP request.
- Use URL-safe Base64 (replace + with -, / with _, strip padding) for URLs and JWT tokens.
- Base64 is not encryption —use it for transport compatibility, not for confidentiality.
- Use our Base64 Encoder and Decoder for instant, private conversion in your browser.