JSON Size Calculator measures the byte size of a JSON payload in both its formatted and minified forms. Paste your JSON to see exactly how many bytes it takes in UTF-8 encoding — useful for checking against API payload limits, cache entry size limits, or database field constraints before deploying.
The calculator measures byte size using UTF-8 encoding, which is the standard encoding for JSON. For ASCII-only JSON (typical API payloads with English strings and numbers), each character is one byte. Unicode characters outside the ASCII range — such as accented letters, CJK characters, or emoji — take 2 to 4 bytes each. The tool shows both the raw size with formatting and the size after minification so you can see how much whitespace contributes.
Yes. The tool shows the size of the JSON as you pasted it (with your current indentation and line breaks) and also the size after minification. The difference between the two shows how much space the formatting whitespace takes up.
UTF-8, which is the standard encoding for JSON. For most developer payloads with ASCII characters (letters, numbers, punctuation), each character is one byte. If your JSON contains emoji or non-Latin characters, those take 2 to 4 bytes each, and the calculator accounts for this accurately.
Network transfer size in DevTools reflects the compressed (gzip or Brotli) size, which is typically 60-80% smaller than the uncompressed byte size. This calculator shows uncompressed byte count. The actual transfer size depends on your server's compression settings.
No. The calculation runs entirely in your browser. Your JSON is never uploaded.
Tool workspace
Free JSON Size Calculator online — instantly measure JSON payload size in bytes. Identify data bloat and verify against API size limits. No login.
Output
Input
{"data": null}Output
Size: 14 Bytes (minified) / 19 Bytes (pretty)