The number of rows in a truth table depends on the number of inputs:
| Number of Inputs | Formula | Number of Rows | Example Combinations |
|---|---|---|---|
| 1 | 2¹ | 2 | 0, 1 |
| 2 | 2² | 4 | 00, 01, 10, 11 |
| 3 | 2³ | 8 | 000, 001, 010, 011, 100, 101, 110, 111 |
| 4 | 2⁴ | 16 | 0000 through 1111 |
Memory trick: Each input DOUBLES the number of rows. 1 input = 2 rows, 2 inputs = 4 rows, 3 inputs = 8 rows, etc.
This key facts covers Truth Table Size Reference within Truth Tables for GCSE Computer Science. Revise Truth Tables in 3.4 Computer Systems for GCSE Computer Science with 15 exam-style questions and 15 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 8 of 11 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Truth Tables
How many rows are needed in a truth table with 2 inputs (not including the header row)?
Explain why truth tables are useful when designing or testing logic circuits.