Two's complement of -8
The number -8 in 8-bit two's complement is 11111000. You get it by taking the two's complement of 8: write 8 in binary as 00001000, invert every bit to 11110111, then add 1. Applying the two's-complement operation to -8 negates it back to 8 (00001000).
Invert and add 1
Here is how -8 is written in 8-bit two's complement, step by step. You take the two's complement of the magnitude 8:
- Write 8 in 8-bit binary:
00001000. - Invert every bit (the one's complement):
11110111. - Add 1:
11111000.
-8 at 4, 8, and 16 bits
| Width | -8 as a signed number | Two's complement of -8 |
|---|---|---|
| 4-bit | 1000 | — |
| 8-bit | 11111000 | 00001000 |
| 16-bit | 1111111111111000 | 0000000000001000 |
A dash means -8 (or its negation) is outside that width's signed range: 4-bit two's complement holds -8 to 7, 8-bit holds -128 to 127, and 16-bit holds -32768 to 32767.
Convert any number
Two's complement is how computers store signed integers, so one adder can both add and subtract. Read the full two's complement lesson, or convert any value at 8, 16, or 32 bits with the two's complement calculator.
Want to see two's complement do real work? Open the lab and wire a subtractor from an adder and inverters, or follow the free course from a transistor up to an 8-bit CPU.
Open the two's complement calculator →Frequently asked
What is the two's complement of -8?
Applying the two's-complement operation to -8 negates it to 8 (00001000 in 8-bit binary). The pattern 11111000 is how -8 itself is stored in 8-bit two's complement.
How do you write -8 in two's complement?
-8 in 8-bit two's complement is 11111000: write 8 as 8-bit binary, invert the bits, and add 1. At 16 bits it is 1111111111111000.
What is -8 in 16-bit two's complement?
-8 in 16-bit two's complement is 1111111111111000. Two's complement sign-extends a shorter value by copying the sign bit to the left, so the value is unchanged from its 8-bit form.