NOR gate
A NOR gate is an OR gate with its output inverted: the output is 1 only when all inputs are 0. Its symbol is the OR gate’s shape with a small circle at the output.
Easily confused with
How to read it
Kuphaldt’s Lessons in Electric Circuits describes the NOR gate as an OR gate with its output inverted, the way a NAND gate is an AND gate with an inverted output: the output goes low if any input is high. In Boolean algebra NOR is an OR with a bar over the whole expression, NOT (A + B): Texas Instruments’ data sheet for the SN74HC02, four 2-input NOR gates, gives each gate’s function as A + B with the bar across it. Unicode encodes ⊽ as NOR. Like NAND, NOR is a universal gate: enough NOR gates can mimic any other gate.
Also searched as: 7402, NOR gate symbol, NOR gate truth table, NOT OR, universal gate.
Truth table
| A | B | Y = NOT (A + B) |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
The two standard shapes
Distinctive shape ANSI/IEEE Std 91: the OR shape with a circle. Rectangular shape IEC 60617-12: a box marked ≥1, with a circle at the output.
The same gate drawn as an AND
An AND gate with bubbles on both inputs, which Kuphaldt calls a negative-AND gate, has the same truth table as a NOR gate. Kuphaldt notes that it is not the same as a NAND gate, contrary to most people’s first instinct.
Look-alikes
The OR gate is the same shape without the circle, and the XNOR gate adds a second curved line behind the back.
Read next
- Next in Logic gate symbolsXOR gateAn XOR (exclusive OR) gate’s output is 1 when its inputs differ and 0 when they are the same. Its symbol is the OR gate’s shape with a second curved line behind its back.
- The same shape in Air Force ranksChief master sergeant (E-9)Chief master sergeant, pay grade E-9: the highest of the senior noncommissioned officer ranks in the US Air Force. The insignia is five stripes below a star in a circle and three stripes above it.
More logic gate symbols
The same shape elsewhere
Browse symbols drawn with circles, curves and waves or lines.
Sources
- Lessons In Electric Circuits, Volume IV: Digital, chapter 3, Logic Gates, Tony R. Kuphaldt, open textbook (Design Science License), Tony R. Kuphaldt (ibiblio), The NOR gate; The Negative-AND gate; Gate universality
- SNx4HC02 Quadruple 2-Input Positive-NOR Gates (data sheet), SN74HC02 data sheet, Texas Instruments, 3 Description
- Overview of IEEE Standard 91-1984: Explanation of Logic Symbols, SDYZ001A, 1996, Texas Instruments, Table 1; Table 2
- Mathematical Operators, Range: 2200–22FF (code chart), The Unicode Standard, Unicode Consortium, U+22BD
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research
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