NTAG213
139 of 144 B writable
106 B remaining
5 B factory lock TLV
Payload input
What will the tag store?
Detected: URL → URI record
33 chars · 33 B
Whitespace around the URL is trimmed and a standard http(s) prefix is stored as a 1-byte code, exactly as phones write it.
Bytes written to the tag
33bytes
NDEF record + Type 2 TLV + terminator
Compared against each chip’s writable NDEF area, not its advertised size
Chip fit
Fits
NTAG215
496 of 504 B writable
463 B remaining
8 B hidden by CC
NTAG216
872 of 888 B writable
839 B remaining
16 B hidden by CC
Memory map
Where your 33 bytes land on each NTAG21x EEPROM. The advertised user memory is larger than what a phone can write: NTAG213 carries a 5-byte factory Lock Control TLV, and NTAG215/216 declare 496 and 872 bytes in their Capability Container.
NTAG213
144 B user memory · 139 B writable NDEF
FitsRecommended
EEPROM layout
page 04hpage 27h
0 B139 B
▧ Lock TLV 5 B33 B requested106 B remaining
144 B user memory − 5 B Lock TLV − 0 B CC-hidden = 139 B writable NDEF. CC and CFG blocks sit outside user memory; shown at fixed width.
NTAG215
504 B user memory · 496 B writable NDEF
Fits
EEPROM layout
page 04hpage 81h
0 B496 B
33 B requested463 B remaining▧ CC-hidden 8 B
504 B user memory − 0 B Lock TLV − 8 B CC-hidden = 496 B writable NDEF. CC and CFG blocks sit outside user memory; shown at fixed width.
NTAG216
888 B user memory · 872 B writable NDEF
Fits
EEPROM layout
page 04hpage E1h
0 B872 B
33 B requested839 B remaining▧ CC-hidden 16 B
888 B user memory − 0 B Lock TLV − 16 B CC-hidden = 872 B writable NDEF. CC and CFG blocks sit outside user memory; shown at fixed width.
Recommendation
NTAG213 is the smallest chip this fits on.
NTAG213 is the smallest chip whose writable NDEF area (139 of 144 bytes) fits the 33-byte record, with 106 bytes to spare.
Guide rule of thumb: URL under 50 characters → NTAG213 (144 bytes) with room to spare
Byte breakdown
- Input content (UTF-8)
- 33 B
- URI identifier code
- 1 B
- “https://” stored as a 1-byte code (0x04): 8 B replaced by 1 B (7 B saved).
- Stored URI remainder
- 25 B
- NDEF payload
- 26 B
- NDEF record header
- 4 B
- 1 B flags + 1 B type length + 1 B payload length + 1 B type “U”.
- Complete NDEF record
- 30 B
- Type 2 TLV wrapper
- 3 B
- 1 B 0x03 type + 1 B length + 1 B 0xFE terminator.
Total bytes needed33 B
Advertised vs writable
What each chip really holds
Figures from the NXP NTAG213/215/216 product data sheet (Rev 3.2, section 8.5). The last two columns are derived from the same byte model the calculator uses, for ASCII content.
| Chip | User memory | CC byte 2 | Reserved | Writable NDEF | Max https URL | Max text |
|---|---|---|---|---|---|---|
| NTAG213 | 144 Bpages 04h–27h | 12h= 144 B | 5 B lock TLV | 139 B | 139 chars | 129 chars |
| NTAG215 | 504 Bpages 04h–81h | 3Eh= 496 B | 8 B hidden by CC | 496 B | 491 chars | 481 chars |
| NTAG216 | 888 Bpages 04h–E1h | 6Dh= 872 B | 16 B hidden by CC | 872 B | 867 chars | 857 chars |
CC byte 2 × 8 = bytes declared for NDEF. NTAG213 declares all 144 bytes but ships with a 5-byte Lock Control TLV (01 03 A0 0C 34) ahead of the NDEF TLV, which writers preserve. NTAG215/216 declare 496 and 872 bytes, leaving 8 and 16 bytes of user memory unused by NDEF.
Calculation model
What the estimate counts
One NDEF record is placed inside an NFC Forum Type 2 Tag TLV. The calculation models the fields listed here.
URI prefix compression
Standard http and https prefixes use one identifier byte, so the repeated prefix text does not have to be stored in full.
NDEF record overhead
The estimate includes the payload, record flags, type, type length and the short or long payload-length field.
Type 2 TLV wrapper
The estimate adds the NDEF TLV type, its one- or three-byte length field, and a terminator byte.
Writable area, not advertised size
Fit is checked against the bytes a phone can actually write: 139 on NTAG213, 496 on NTAG215 and 872 on NTAG216, per the NXP datasheet.
Need the decision rules and encoding cautions? Read the full memory and payload guide.