CRC8 Calculator

Calculate an 8-bit CRC for text or hex bytes. The table under the calculator shows all 20 CRC-8 variants for your input, so you can match the one your sensor, bus or protocol uses. CRC8 計算（日本語）

9 bytes

Text encodingLine endings

Algorithm

Width (bits)PolynomialInitial valueFinal XOR

Reflect inputReflect output

ResultCRC-8

Uppercase0x prefix

0xF4

Decimal: 244
Binary: 11110100
Bytes, big-endian: F4
Bytes, little-endian: F4

Check value for "123456789": 0xF4

Source code for this CRC

Generated for the parameters above. Bit-by-bit and table-free, so it is easy to port to a microcontroller.

#include <stddef.h>
#include <stdint.h>

uint8_t crc_8(const uint8_t *data, size_t len)
{
    uint8_t crc = 0x00;
    while (len--) {
        crc ^= (uint8_t)*data++;
        for (int i = 0; i < 8; i++)
            crc = (crc & 0x80) ? (crc << 1) ^ 0x07 : crc << 1;
    }
    return crc;
}

All CRC algorithms for this input

Click a row to load its parameters into the calculator.

Result	Poly	Init	RefIn	RefOut	XorOut	Check	Used in
0xF4	0x07	0x00	false	false	0x00	0xF4	SMBus PEC, I2C sensors
0xA1	0x31	0x00	true	true	0x00	0xA1	Dallas/Maxim 1-Wire (DS18B20)
0xD0	0x07	0xFF	true	true	0x00	0xD0	Robust Header Compression
0xA1	0x07	0x00	false	false	0x55	0xA1	ATM HEC (ITU-T I.432.1)
0x4B	0x1D	0xFF	false	false	0xFF	0x4B	Automotive SAE J1850, AUTOSAR E2E
0xDF	0x2F	0xFF	false	false	0xFF	0xDF	AUTOSAR E2E profiles
0xDA	0x9B	0xFF	false	false	0x00	0xDA	CDMA2000 mobile
0x15	0x39	0x00	true	true	0x00	0x15	Data Radio Channel
0xBC	0xD5	0x00	false	false	0x00	0xBC	DVB-S2 baseband header
0x97	0x1D	0xFF	true	true	0x00	0x97	AES3 / EBU digital audio
0x7E	0x1D	0xFD	false	false	0x00	0x7E	Philips I-CODE RFID
0x25	0x9B	0x00	true	true	0x00	0x25	WCDMA mobile
0x26	0xA7	0x00	true	true	0x00	0x26	Bluetooth HEC
0xEA	0x9B	0x00	false	false	0x00	0xEA	LTE (3GPP TS 36.212)
0xF7	0x31	0xFF	false	false	0x00	0xF7	HD Radio, Sensirion SHT sensors
0x3E	0x2F	0x00	false	false	0x00	0x3E	openSAFETY
0x37	0x1D	0x00	false	false	0x00	0x37	GSM
0x94	0x49	0x00	false	false	0xFF	0x94	GSM
0xB4	0x1D	0xFF	false	false	0x00	0xB4	HITAG RFID
0x99	0x1D	0xC7	false	false	0x00	0x99	MIFARE application directory

Common CRC8 variants

An 8-bit CRC protects short messages: a sensor reading, a command byte, a packet header. Because every vendor picked its own parameters, "CRC8" covers a family of incompatible algorithms. The check value is the CRC of the ASCII string 123456789.

Variant	Poly	Init	Reflected	XorOut	Check	Used in
CRC-8 (SMBus, ATM)	`07`	`00`	no	`00`	`F4`	SMBus PEC, I²C sensors, MLX90614
CRC-8/MAXIM	`31`	`00`	yes	`00`	`A1`	1-Wire: DS18B20, iButton
CRC-8/NRSC-5	`31`	`FF`	no	`00`	`F7`	Sensirion SHT3x, SCD4x, SGP
CRC-8/SAE-J1850	`1D`	`FF`	no	`FF`	`4B`	OBD, AUTOSAR E2E profile 1
CRC-8/AUTOSAR	`2F`	`FF`	no	`FF`	`DF`	AUTOSAR E2E profile 2
CRC-8/ROHC	`07`	`FF`	yes	`00`	`D0`	Robust Header Compression
CRC-8/ITU	`07`	`00`	no	`55`	`A1`	ATM header error control
CRC-8/DVB-S2	`D5`	`00`	no	`00`	`BC`	DVB-S2, CRSF radio link
CRC-8/BLUETOOTH	`A7`	`00`	yes	`00`	`26`	Bluetooth header check

CRC8 in C

The plain CRC-8 with polynomial 0x07. For another non-reflected variant, change the polynomial, the starting value and the final XOR.

uint8_t crc8(const uint8_t *data, size_t len)
{
    uint8_t crc = 0x00;
    while (len--) {
        crc ^= *data++;
        for (int i = 0; i < 8; i++)
            crc = (crc & 0x80) ? (crc << 1) ^ 0x07 : crc << 1;
    }
    return crc;
}

Reflected variants such as CRC-8/MAXIM shift the other way and use the bit-reversed polynomial (0x8C for 0x31):

uint8_t crc8_maxim(const uint8_t *data, size_t len)
{
    uint8_t crc = 0x00;
    while (len--) {
        crc ^= *data++;
        for (int i = 0; i < 8; i++)
            crc = (crc & 1) ? (crc >> 1) ^ 0x8C : crc >> 1;
    }
    return crc;
}

The calculator above generates the matching C, Python and JavaScript for whichever variant is selected.

Test vectors

Input	Variant	CRC
`BE EF` (hex)	CRC-8/NRSC-5 (Sensirion)	`92`
`hello`	CRC-8	`92`
`hello`	CRC-8/MAXIM	`13`
`hello`	CRC-8/SAE-J1850	`A9`

For longer frames use a wider check: the CRC16 calculator covers CCITT, MODBUS and XMODEM, the CRC32 calculator covers CRC-32 and CRC-32C, and the CRC64 calculator covers the 64-bit variants. If your protocol uses a plain sum or XOR instead of a CRC, try the checksum calculator.

Frequently asked questions

Which CRC8 polynomial is the standard one?

There is no single standard. The plain "CRC-8" uses polynomial 0x07 with initial value 0 and no reflection; it is the SMBus packet error code and is also called CRC-8/ATM or CRC-8/CCITT. Dallas/Maxim 1-Wire devices use 0x31 reflected, and automotive systems use 0x1D (SAE J1850) or 0x2F (AUTOSAR). Check your datasheet for the polynomial and the initial value.

What is the CRC8 of "123456789"?

It depends on the variant: 0xF4 for plain CRC-8, 0xA1 for CRC-8/MAXIM, 0x4B for CRC-8/SAE-J1850, 0xDF for CRC-8/AUTOSAR and 0xD0 for CRC-8/ROHC. These check values are the fastest way to confirm which variant a piece of code implements.

How do I calculate the CRC for a Sensirion SHT3x or SCD4x sensor?

Sensirion sensors use polynomial 0x31, initial value 0xFF, no reflection and no final XOR — listed here as CRC-8/NRSC-5. The datasheet test vector is the two bytes BE EF, which give 0x92. Each 16-bit word read from the sensor is followed by its own CRC byte.

What is the difference between polynomial 0x31 and 0x8C?

They are the same polynomial written in opposite bit orders: 0x8C is 0x31 reflected. Code that shifts right, as 1-Wire implementations do, stores it as 0x8C. Likewise 0xE0 is the reflected form of 0x07.

How reliable is an 8-bit CRC?

It detects every single-bit error and every burst up to 8 bits long, and lets about 1 in 256 of other corruptions through. That is fine for a few bytes on a short bus, which is where CRC-8 is used. For longer messages use CRC-16 or CRC-32.