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.
Truth Table Size Reference
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.
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.