Even parity is the more common of the two parity conventions. The rule is easy to remember: after adding the parity bit, the message must contain an even number of 1s. If the data already has an even count – including zero 1s – the parity bit is 0; if the count is odd, the parity bit is 1. In other words, the even parity bit is simply the XOR of all the data bits.
That XOR property makes even parity cheap in hardware: a chain of XOR gates produces it, and a receiver that XORs all incoming bits including the parity bit expects a result of 0. RAID 5 uses exactly this idea across disks – the parity block is the XOR of the data blocks, so any one lost block can be rebuilt. Serial links configured as 7E1 or 8E1 send an even parity bit after every character.
Like every single parity bit, even parity notices any odd number of flipped bits but misses an even number of them, and it never tells you where the error is. Enter several bytes separated by spaces to see a parity bit for each.
How to use the Even Parity Calculator
- What to do
- Binary message — Several messages (e.g. bytes) can be separated by spaces.
- Parity bit position — 0 = at the end. Otherwise the position counted from the left (1 = first bit).
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How it works
The 1s in each message are counted; the parity bit is 1 if the count is odd and 0 if it is even. In check mode a message passes when its total number of 1s is even.
Worked example
Message 1001011: the 1s are in positions 1, 4, 6 and 7 – four in total, an even number – so the even parity bit is 0 and the transmitted message is 10010110. For 1010111 (five 1s) the bit would be 1, giving 10101111.
Even parity truth table for 3 bits
| Data | 000 | 001 | 010 | 011 | 100 | 101 | 110 | 111 |
|---|---|---|---|---|---|---|---|---|
| Parity bit | 0 | 1 | 1 | 0 | 1 | 0 | 0 | 1 |
Formula
Even parity bit = (number of 1s in the data) mod 2
Valid message: total number of 1s (data + parity bit) is even
Worked example
Inputs — What to do: Generate – add a parity bit; Binary message: 1001011; Parity bit position: 0.
Results — Result = 10010110; Verdict = Parity bit added for even parity – every message now has an even number of 1s; Parity bit(s) = 0; Number of 1s in the input = 4; Messages = 1; Message by message = Message 1s Parity bit Transmitted
───────────────────────────────────────
1001011 4 0 10010110.
Key terms
- Even parity
- Convention in which every valid message has an even number of 1s.
- XOR
- Exclusive OR; the XOR of all bits equals the even parity bit.
- 7E1 / 8E1
- Serial settings with 7 or 8 data bits, even parity and 1 stop bit.
Frequently asked questions
How do I calculate an even parity bit?
Count the 1s. If the count is odd the bit is 1, if it is even the bit is 0 – equivalently, XOR all the bits.
What is the even parity bit of 1001011?
It has four 1s (even), so the bit is 0 and the message becomes 10010110.
Is 0000 even parity?
Yes – zero 1s is an even number, so the parity bit is 0.
Is 1010110 valid with even parity?
It has four 1s, so yes – no error is detected.
What is the difference between even and odd parity?
Only the target count: even parity makes the total number of 1s even, odd parity makes it odd. Their parity bits are always opposite.