OR gate using NOR gates: two gates, live

An OR gate takes two NOR gates: the first computes NOR(A, B), and the second, with both inputs tied together, inverts it. NOT NOR(A, B) = A OR B, so Y is 1 whenever A or B is 1.

NOR means NOT OR, so getting OR back only needs one more inversion, and a NOR gate with its inputs joined is an inverter: NOR(X, X) = NOT X. That makes OR the cheapest gate to build from NORs after NOT itself. The mirror of this circuit is the AND gate from two NAND gates. AND from NORs takes three gates (AND from NOR gates), and the NOR universal gates page builds NOT, OR, AND and XOR side by side.

Live circuit: click the inputs to toggle them and watch the outputs update. It runs the real simulator, right here on the page.

Open this circuit in the lab →

Embed or cite this circuit

Free to embed on a course page, blog or worksheet: paste this code. The circuit stays live, and the small digiwleea badge links back here.

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To cite it: digiwleea, “OR gate from NOR gates”, https://digiwleea.wleeaf.dev/tools/build/or-from-nor/

What you need

1× NOR: N = NOR(A, B)
1× NOR: Y = NOR(N, N) = A OR B

Step by step

Place inputs A and B and a probe Y.
Feed A and B into the first NOR gate.
Feed its output into both inputs of a second NOR gate and probe that as Y.
Try all four rows: Y is 0 only when A and B are both 0.

OR from NOR truth table

A	B	N = NOR(A, B)	Y = A OR B
0	0	1	0
0	1	0	1
1	0	0	1
1	1	0	1

All input rows are checked on the live circuit before the page is built.

You can also read the full theory in the lesson on NOR as a universal gate. Prefer to build it yourself from scratch? Open the digiwleea lab and place the gates on the canvas, or start from the logic gate simulator.

More builds: Universal gates: NAND only, NOR only

NOR gate from NAND gates AND gate from NOR gates OR gate from NAND gates XOR gate from NOR gates AND gate from NAND gates XNOR gate from NOR gates NOT gate from a NOR gate half adder from NAND gates NOT gate from a NAND gate full adder from NAND gates XNOR gate from NAND gates half subtractor from NAND gates

All 246 build guides, by topic

Each of these is one step from a transistor to a working CPU. Build every gate from CMOS transistors and work all the way up in the free digiwleea lab, with the free theory reference alongside.

Open the OR gate from NOR gates in the lab →

Frequently asked

How many NOR gates are needed to make an OR gate?

Two: one NOR gate, then a second NOR gate with its inputs tied together to invert the result. NOT NOR(A, B) = A OR B.

How do you make a NOT gate from a NOR gate?

Tie both inputs of the NOR gate together, or tie one input to 0. NOR(A, A) = NOT A.

How many NOR gates make an AND gate?

Three: two NORs invert A and B, and a third NORs the inverted inputs, NOR(NOT A, NOT B) = A AND B.