Round a number to significant figures or decimals, and count its sig figs.
Calculated instantly in your browser.
How do you count and round to significant figures?
Significant figures are counted from the first non-zero digit. Leading zeros are never significant; trailing zeros count only when a decimal point is present. Rounding to sig figs keeps the most meaningful digits, showing how precise a measurement is. For example, 3.14159 rounded to 3 significant figures is 3.14, and 12,345 to 2 sig figs is 12,000.
Understanding your result
Significant figures show how precise a measurement is. Rounding to sig figs keeps the most meaningful digits, while decimal-place rounding fixes the number of digits after the point regardless of magnitude.
Formula and method
Significant figures are counted from the first non-zero digit. Leading zeros are never significant; trailing zeros count only when a decimal point is present.
Assumptions and limitations
This tool rounds to a chosen number of significant figures or decimal places and counts the significant figures in your input, following standard rules. Ambiguity remains for trailing zeros in whole numbers without a decimal point, such as 1200; scientific notation removes that doubt. It applies rounding mechanically and does not track measurement uncertainty through calculations.
Worked example
3.14159 rounded to 3 significant figures is 3.14; 12,345 to 2 sig figs is 12,000.
How to use this tool
- Enter your number.
- Choose significant figures or decimal places.
- Set how many and read the rounded value.
Common mistakes to avoid
- Counting leading zeros as significant.
- Assuming trailing zeros in a whole number are significant without a decimal point.
About the Significant Figures Calculator
The Significant Figures Calculator rounds a number to a chosen number of significant figures or decimal places, counts the significant figures in your input, and shows the scientific-notation form.
Who should use this tool
Science and engineering students, lab workers and anyone reporting measurements correctly.
Benefits
- Round to significant figures or decimal places.
- Counts the sig figs in your number.
- Shows the scientific-notation form.
- Handles very large and very small numbers.
Practical use cases
- Reporting a measurement to the right precision.
- Rounding a result for a lab write-up.
- Checking how many sig figs a value has.
Frequently asked questions
Are trailing zeros significant?
Only when there is a decimal point. 100 has one or two ambiguous sig figs, but 100.0 clearly has four.
What is the difference from decimal places?
Significant figures count meaningful digits from the first non-zero one; decimal places count digits after the decimal point only.
How does it count significant figures in a number like 1200?
Trailing zeros in a whole number with no decimal point are ambiguous, so their significance cannot be determined from the digits alone. The tool applies the common convention that such trailing zeros are not counted unless a decimal point is present. Writing the value in scientific notation, such as 1.20 times 10 cubed, states the precision clearly.