Significant Figures Calculator
Count and round sig figsRuns locally · nothing uploaded
Significant figures
5
Significant digits
45600
Rounded (3 sig figs)
0.00456
Scientific notation
4.56 × 10⁻³
How it works
When to use it
- Check sig figs in lab data or homework.
- Round a result to a given number of significant figures.
Formula
All non-zero digits count; zeros between them count1002 has 4.
Leading zeros never count0.0045 has 2.
Trailing zeros count after a decimal point; in whole numbers they're ambiguous2.50 has 3; write 1200 in scientific notation to be clear.
Worked example
Given: 0.0045600, round to 3 sig figs
- Leading 0.00 doesn't count; 4, 5, 6 and the two trailing zeros do.
- That's 5 significant figures.
- Rounded to 3: 0.00456 (4.56 × 10⁻³).
Result: 5 sig figs; 0.00456 to three.
Reading the result
- Multiplying or dividing: keep the fewest sig figs of the inputs. Adding or subtracting: keep the fewest decimal places.
Limitations
- Rounds half up using binary floating point, so a few values (e.g. 1.005 to 3 sig figs) show as 1.00. Some standards use round-half-to-even, which differs when the dropped digit is exactly 5.
- Exact numbers (counts, defined constants) have unlimited sig figs.
How to use
- 1Enter a number (scientific notation like 6.02e23 is fine).
- 2Read the sig fig count.
- 3Choose how many to keep and read the rounded value.
FAQ
How do I count significant figures?
Start at the first non-zero digit and count to the last digit. Trailing zeros after a decimal point count.
How many sig figs in 1200?
It is ambiguous (2 to 4). Write 1.20 × 10³ to make it explicit.