Two's complement of 15
The 8-bit two's complement of 15 is 11110001, the bit pattern that represents -15 (minus 15). Written as a signed 8-bit number, 15 itself is 00001111.
Invert and add 1
Here is the two's complement of 15 at 8 bits, step by step (invert the bits of 15 and add 1):
- Write 15 in 8-bit binary:
00001111. - Invert every bit (the one's complement):
11110000. - Add 1:
11110001.
15 at 4, 8, and 16 bits
| Width | 15 as a signed number | Two's complement of 15 |
|---|---|---|
| 4-bit | — | — |
| 8-bit | 00001111 | 11110001 |
| 16-bit | 0000000000001111 | 1111111111110001 |
A dash means 15 (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 15?
The 8-bit two's complement of 15 is 11110001, the bit pattern for -15. You get it by writing 15 in binary (00001111), inverting every bit (11110000), then adding 1.
How do you write 15 in two's complement?
15 in 8-bit two's complement is 00001111. Positive numbers are identical to plain binary, so no inverting is needed. At 16 bits it is 0000000000001111.
What is 15 in 16-bit two's complement?
15 in 16-bit two's complement is 0000000000001111. 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.