NDEF Capacity Calculator
Live check: does your URL / text / vCard / Wi-Fi payload fit on your chosen NFC chip? NDEF framing and URI-prefix compression are applied.
Type 5. Raw area: 512 B; modeled capacity: 512 B.
Prefix https:// compressed to 1 byte (code 0x04). Remainder stored: roxtron.com/rfid
How this calculator works
This estimator counts one NDEF record using UTF-8, short-record headers for payloads below 256 bytes, and URI-prefix compression. Type 2 and Type 5 layouts use a message TLV and a terminator; Type 4 uses a two-byte NLEN inside the NDEF file. Type 5 examples also reserve their Capability Container. Actual writable space depends on the tag's CC, file configuration, lock/control TLVs and existing records. Enter additional reserved bytes for your formatter and confirm the result with your target reader or phone. This is a capacity estimate, not a tag writer.
Sources: NXP NTAG21x, NTAG 424 DNA, and ST AN4911. Model reviewed 17 October 2026.
URI prefix table
If your URL starts with one of these strings, a single byte replaces the whole prefix.
FAQ
Why can raw user memory exceed writable NDEF space?
NDEF framing, the advertised memory area, formatting metadata and application configuration all consume or restrict space. The selected example lists its assumptions.
Are bytes the same as characters?
No. UTF-8 characters can occupy multiple bytes. The calculator counts encoded bytes, including the language code for text records.
Will any phone accept a Wi-Fi record?
No. This models one WSC credential. Operating-system support and optional vendor fields vary; test the actual deployment.