How to count significant figures
- Type the number exactly as written, keeping any trailing zeros and the decimal point: 0.004560, 1200 or 1.20e3.
- Read how many significant figures it has and which rule decided it.
- To round, enter how many significant figures you want under Round to.
Examples
| Number | Significant figures | Why |
|---|---|---|
| 45.6 | 3 | All non-zero digits count |
| 0.0045 | 2 | Leading zeros don’t count |
| 1005 | 4 | Zeros between digits count |
| 4.50 | 3 | Trailing zero after a decimal point counts |
| 1200 | 2 | Trailing zeros in a whole number are ambiguous |
| 1.20 × 10³ | 3 | Scientific notation shows them exactly |
Why they matter
Significant figures show how precisely something was measured. A scale that reads 4.50 g promises more than one that reads 4.5 g, and an answer can’t be more precise than the measurements it came from. That’s why chemistry and physics classes ask for answers to a given number of significant figures.