String Length Calculator

UTF-8 is variable-width: ASCII characters use 1 byte, Latin/accented characters use 2 bytes, most CJK characters use 3 bytes, and emoji use 4 bytes. UTF-16 is also variable but uses a minimum of 2 bytes: ASCII characters use 2 bytes, most characters use 2 bytes, and characters outside the Basic Multilingual Plane use 4 bytes. So ASCII text is always half the size in UTF-8 vs UTF-16. CJK text is often the same size or smaller in UTF-16.

URL encoding (percent-encoding) converts special characters and non-ASCII characters to %XX format. The space character becomes %20 (3 chars), adding 2 extra chars per space. A character like é becomes %C3%A9 (6 chars), expanding significantly. This measurement shows the length after full URL encoding — useful for checking if a query parameter or path segment will exceed length limits (browsers enforce 2,048-8,000 chars for full URLs depending on the browser).

Base64 encoding converts binary data to ASCII text for safe transmission. Every 3 bytes of input become 4 Base64 characters. The formula is ceil(bytes / 3) * 4, padded to a multiple of 4. A 10-byte UTF-8 string becomes approximately 16 Base64 characters. This measurement is useful when calculating API payload sizes, email attachment sizes, or data URI lengths.

JavaScript uses UTF-16 encoding internally. The .length property counts UTF-16 code units, not characters. For all ASCII and most Latin text, .length equals the character count. But emoji and characters in Unicode planes above U+FFFF require 2 UTF-16 code units (a surrogate pair) — so .length over-counts them. Use Array.from(str).length or [...str].length for accurate character (code point) counting.

It depends on the emoji. A simple emoji like 😊 (U+1F60A): 2 UTF-16 code units, 1 code point, 4 UTF-8 bytes. A flag emoji like 🇩🇪: 4 UTF-16 code units, 2 code points, 8 UTF-8 bytes. A skin-tone modifier emoji like 👋🏽: 4 UTF-16 code units, 2 code points, 8 UTF-8 bytes. A family emoji (👨‍👩‍👧) built from ZWJ sequences: many code units and code points. The tool counts each layer correctly.

A Unicode code point is a number assigned to a character (e.g., U+1F60A for 😊). A code unit is the storage unit for a specific encoding — UTF-8 uses 8-bit units, UTF-16 uses 16-bit units. Most characters fit in one UTF-16 code unit (the Basic Multilingual Plane, U+0000–U+FFFF). Characters outside this range (emoji, some historical scripts) require two UTF-16 code units (a surrogate pair).

No. All length calculations run locally in your browser via JavaScript. Paste API keys, passwords, or sensitive text without concern — nothing is transmitted anywhere.