Significant figures calculator
Type a number exactly as written, including trailing zeros and any decimal point. You get its count of significant figures and the number rounded to the sig figs you choose, in plain form and in scientific notation.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter the number as it was measured or given, keeping trailing zeros and the decimal point.
- Read the count of significant figures.
- Choose how many figures to round to; the rounded number appears in plain and scientific form.
How it works
The text you typed is inspected, not converted to a floating-point value, because 1.20 and 1.2 are the same value but have different precision. The digits are stripped of leading zeros; then trailing zeros are kept if there is a decimal point and dropped if there is none. Rounding uses the exact decimal digits and the half-up rule.
Worked examples
| Number |
Sig figs |
Why |
| 0.00120 |
3 |
Leading zeros out, trailing zero after the point in |
| 1200 |
2 |
Whole number, trailing zeros are placeholders |
| 1200. |
4 |
The point makes the zeros significant |
| 100.5 |
4 |
Zeros between digits count |
| 1.200e3 |
4 |
Coefficient digits |
Rounding 0.004560 to 3 figures gives 0.00456 (4.56 × 10^-3).
Tips
- The result of multiplying or dividing measured values should keep as many sig figs as the least precise input.
- For addition and subtraction, the rule works on decimal places instead, so the rounding calculator is the better fit there.
Frequently asked questions
What are the rules for counting significant figures?
Non-zero digits always count. Zeros between non-zero digits count (100.5 has 4). Leading zeros never count (0.0305 has 3). Trailing zeros count when the number has a decimal point (0.00120 has 3, and 1200. has 4), but not in a whole number written without one (1200 has 2).
Why is 1200 shown as 2 significant figures?
By the usual convention, trailing zeros before an unwritten decimal point are placeholders and may or may not be measured. The tool takes the cautious reading and shows a reminder. Write 1200. or 1.200 × 10^3 to say that all four digits are significant.
How does rounding to significant figures work?
Keep the first N digits starting from the first non-zero digit and round the rest half up. 3.14159 to 3 sig figs is 3.14, 1234 to 2 is 1200, and 0.000456 to 2 is 0.00046. Trailing zeros are kept so the result shows its precision: 1.5 to 3 sig figs is 1.50.
How are zero and scientific notation counted?
In scientific notation only the coefficient is counted, so 1.200e3 and 3 x 10^5 have 4 and 1 significant figures. The number 0 is counted as 1.
What happens when rounding carries over, like 9.996?
9.996 to 3 sig figs becomes 10.0. The carry adds a digit on the left, so the last digit is dropped to keep exactly three figures.