JSON Size Calculator – Free Online Tool
Measure exact UTF-8 JSON bytes, minified size, whitespace savings, and payload structure.
Measure Exact JSON Size in UTF-8 Bytes
Paste a JSON document or load a local .json file to measure the bytes that its text occupies when encoded as UTF-8. This is more accurate than counting JavaScript string characters because emoji and many non-Latin characters use multiple bytes.
Compare Formatted and Minified JSON
See the current payload, a canonical two-space pretty version, and the minified representation side by side. The whitespace result shows how many bytes formatting adds before transport compression.
Validate JSON Before Measuring a Payload
The analyzer reports parsing errors instead of presenting a misleading minified result. Current text size remains visible so you can distinguish file size from valid JSON structure.
Inspect Keys, Values, Arrays, and Nesting Depth
Review counts for object keys, objects, arrays, strings, numbers, booleans, null values, and maximum nesting depth. These structural signals help explain payload complexity but are not a replacement for API profiling.
Private Local JSON Analysis
Parsing, UTF-8 measurement, validation, file reading, and structural analysis run in your browser. JSON text, local filenames, keys, and values are not uploaded or included in optional analytics.
Frequently Asked Questions
Everything you need to know about the JSON Size Calculator.
How do I calculate JSON size in bytes?
Encode the complete JSON text as UTF-8 and count the resulting bytes. This calculator performs that measurement in your browser.
Why can JSON byte size exceed its character count?
ASCII characters use one UTF-8 byte, while emoji and many international characters use more than one byte.
Does minifying JSON change its data?
Minification removes insignificant whitespace outside strings. It should preserve the parsed data, although serialized key order follows the parser's normal property ordering.
Does this include HTTP headers or gzip compression?
No. Results measure the JSON text itself. HTTP headers, transfer framing, encryption, and content compression can change the number of bytes sent over the network.
Is my JSON uploaded?
No. Pasted JSON and local files are read, parsed, and measured entirely in your browser.