About the Significant Figures Counter
Significant figures are the digits in a number that carry real information about how precisely it was measured. A length written as 0.004500 m has four, while 1,500 on its own could have two, three or four depending on how it was measured. This tool counts the significant figures in any number you type, shows which digits count, and explains when trailing zeros are ambiguous. It can also round the number to a chosen count of sig figs and shows the result in plain and scientific notation, which is what chemistry, physics and engineering courses ask for.
Updated October 2026
How to use the Significant Figures Counter
- 1Type your number exactly as written, keeping all trailing zeros.
- 2Use e notation such as 2.30e4 if the number is in scientific form.
- 3Read how many significant figures it has and which digits are counted.
- 4Enter a number of figures in the second box to round to that precision.
- 5Copy the rounded value or the scientific form.
Why sig figs exist
A ruler marked in millimetres cannot give you a length to the nearest micrometre. Writing too many digits suggests precision you do not have, and writing too few throws precision away. Significant figures are the standard shorthand for the precision of a measurement, and teachers and journals expect answers to match.
When you work through a multi-step calculation, keep one or two extra digits in the middle and round only at the end. Rounding at every step builds up error and can change the last significant figure of the answer. Lab reports and exams usually state the number of sig figs required in the final result, and marks are often lost for giving too many digits as well as too few.
Quick examples
- 45.60 has 4 significant figures, because the trailing zero follows a decimal point.
- 0.0072 has 2, because the leading zeros only place the decimal point.
- 3.0 × 10⁸ has 2, as scientific notation shows exactly what is meant.
- 100 has 1, 100. has 3 and 100.0 has 4.
After counting
Use the Rounding Calculator for decimal places and the Scientific Notation Converter to switch to powers of ten. The Percent Error Calculator compares a measurement with an accepted value, and the Standard Deviation Calculator shows how much repeated measurements vary.
Features
- Counts sig figs including zeros
- Understands scientific notation like 2.30e4
- Rounds to 1 to 21 significant figures
- Shows plain and scientific results
- Flags ambiguous trailing zeros
- Accepts commas in big numbers
Frequently asked questions
What are the rules for significant figures?
All non-zero digits count. Zeros between non-zero digits count. Leading zeros never count. Trailing zeros count only if the number has a decimal point. So 0.004500 has four, 1,005 has four and 1,500 has two unless a decimal point is added.
Do trailing zeros count in a whole number?
It depends on how the number was measured. Without a decimal point, 1500 is ambiguous. Writing 1500. or 1.500 × 10³ makes all four digits significant, while 1.5 × 10³ makes only two significant.
How many significant figures does zero have?
A plain 0 counts as one. Zeros after a decimal point, such as 0.00, count each zero after the point. The calculator follows that convention and counts 0.00 as two.
How do I round to a given number of significant figures?
Count from the first non-zero digit, keep that many digits and round the last one up if the next digit is 5 or more. Rounding 0.004567 to two sig figs gives 0.0046, and 123,456 to two gives 120,000.
Are exact numbers counted?
Exact counts, like 12 eggs in a dozen, and defined constants have unlimited significant figures and never limit the precision of a calculation. Only measured values do.
How are significant figures used in calculations?
In multiplication and division, the answer keeps as many sig figs as the least precise number. In addition and subtraction, the answer keeps as many decimal places as the least precise number.