OR gate truth table
The OR gate outputs 1 when at least one input is 1, and 0 only when both are 0. Here is its full truth table, the boolean expression, and how it is actually built.
| A | B | Y |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
Boolean expression: Y = A + B. A 1 in the table means a high voltage (logic true) and a 0 means low (false). Read each row as: for these inputs, the output Y is this value.
What the OR gate does
OR is logical addition: the output is 1 whenever any input is 1. In CMOS it is a NOR gate followed by an inverter, mirroring how AND is a NAND plus an inverter.
Build it yourself
Reading a table is one thing; watching the signals flow is another. Open the logic gate simulator and wire a OR gate up from transistors, or read the full lesson on how this gate is designed. You can also generate the table for any expression with the truth table generator.
Other gates:
The OR gate is one small step toward a working CPU. Build every gate from CMOS transistors and work up to an 8-bit processor in the free digiwleea lab and course.
Open the gate simulator →Frequently asked
What is the truth table of a OR gate?
The OR gate outputs 1 when at least one input is 1, and 0 only when both are 0. For inputs (A,B) the outputs are 0,0→0 0,1→1 1,0→1 1,1→1.
What is the boolean expression for OR?
The OR gate is written Y = A OR B (symbolically Y = A + B).
How many transistors does a OR gate take?
A standard CMOS OR gate uses about 6 transistors. In digiwleea you build it from those transistors and the simulator verifies it against this exact truth table.