Significant Figures Calculator
Round a number to N significant figures, or count the significant figures in a number.
Significant Figures Calculator
What This Calculator Does
Significant figures are the digits in a number that actually carry meaning about how precisely it was measured. If a scale reads 2.50 kg, all three digits matter - the trailing zero is significant because it shows the weight was measured to the nearest hundredth, not just guessed.
Counting them follows a few rules about which digits “count,” and rounding to a number of significant figures keeps only the most meaningful ones. This tool does both: count the significant figures in a number, or round a number to however many you want.
Significant Figure Rules
- Non-zero digits are always significant.
- Zeros between non-zero digits are significant.
- Leading zeros are NOT significant.
- Trailing zeros are significant only if there is a decimal point.
How to Use It
- Choose round or count.
- Enter the number (and the number of sig figs to keep, when rounding).
- Read the result.
Worked Examples
| Number | Action | Result |
|---|---|---|
| 3.14159 | round to 3 | 3.14 |
| 12345 | round to 2 | 1.2e+4 (12000) |
| 1.2 | round to 4 | 1.200 |
| 1000 | round to 4 | 1000. |
| 0.0012345 | round to 2 | 0.0012 |
| 0.00120 | count | 3 |
| 1023 | count | 4 |
The zeros in 1.200 show four significant figures. A final decimal point makes whole-number precision clear: 1000. has four significant figures. Scientific notation also preserves precision: 1.2e+4 means 1.2 multiplied by 10,000, with two significant figures.
FAQ
What are significant figures?
The digits in a number that carry meaning about its precision — all non-zero digits, zeros between them, and trailing zeros after a decimal point.
How do you round to significant figures?
Keep the chosen number of significant digits, starting from the first non-zero digit, and round the rest. 3.14159 to 3 sig figs is 3.14.
Are trailing zeros significant?
Only when there is a decimal point. “1200” is treated as 2 significant figures, but “1200.” or “120.0” has more.