Significant Figures Calculator
Count the significant figures in a number, or round a number to a chosen number of significant figures.
Change the values and press Calculate to work out your own figures.
Count significant figures
Enter a number exactly as written.
Show the working
- Leading zeros are never significant
- Zeros between nonzero digits are significant
- Trailing zeros after a decimal point are significant
- 0.00120 → 1 2 0 = 3
Round to significant figures
Enter a number and how many significant figures to keep.
Show the working
- Keep the first 2 significant digits; the last kept digit is in the 10,000s place
- Round half away from zero: 120,000
How to use it
Enter a number exactly as written. Enter a number and how many significant figures to keep.
Numbers can be typed with commas and in scientific notation (1.5e3, 1.5 × 10^3 or 1.5×10³). Show the working gives each step.
Key facts
Leading zeros: never significant Zeros between digits: significant Trailing zeros: significant only with a decimal point
Why trailing zeros are ambiguous
1200 could be exact to the nearest hundred or the nearest one. Writing 1200. or 1.200 × 10³ makes all four figures significant; 1.2 × 10³ makes two.
Questions
How many significant figures does 0.00120 have?
3: the leading zeros only place the decimal point; the final zero is measured.
What is 9.99 to 2 significant figures?
10 (1.0 × 10¹).
Formulas
Leading zeros: never significant Zeros between digits: significant Trailing zeros: significant only with a decimal point
Sources
Limitations
- Numbers have at most 400 characters and exponents up to ±10,000 (answers of powers up to ±1,000,000).