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- Counts the significant figures in any number, including trailing zeros.
- Rounds a number to the number of significant figures you choose.
- Shows the result in normal and scientific notation.
- Explains which rule applies, including ambiguous trailing zeros such as in 1200.
How to use the sig fig calculator
Type the number exactly
Include every zero as written, such as 0.004500 or 1200.0. E notation like 6.020e23 also works.
Read the count
The number of significant figures appears, with the significant digits listed.
Round if needed
Open the optional setting and enter how many significant figures you want.
Check the rules
The breakdown shows which sig fig rules were applied.
Significant figure rules
The four rules
1. All non-zero digits are significant
2. Zeros between non-zero digits are significant (100.05 has 5)
3. Leading zeros are never significant (0.0045 has 2)
4. Trailing zeros count only if there is a decimal point (1200 has 2, 1200. has 4, 1200.0 has 5)
In scientific notation, every digit in the coefficient is significant, so 6.020 × 10²³ has 4.
Example 1: counting
How many significant figures?
- 0.004500 4 (4, 5, 0, 0)
- 1200 2 (trailing zeros are ambiguous)
- 1200. 4
- 100.05 5
- 6.020e23 4
Writing 1.200 × 10³ is the clearest way to show that 1200 has four significant figures.
Example 2: rounding
Round to a set number of significant figures.
- 123456 to 3 s.f. 123000 = 1.23 × 10⁵
- 0.004567 to 2 s.f. 0.0046
- 9.996 to 3 s.f. 10.0
The calculator rounds the digits exactly as typed, so there are no floating-point surprises.
Sig figs in calculations
Rules for combining measured values.
- Multiplying or dividing keep the fewest significant figures of the inputs
- Adding or subtracting keep the fewest decimal places of the inputs
Round only the final answer, not each intermediate step.
Where a sig fig calculator helps
Chemistry and physics labs
Report measurements with the right precision for your instruments.
Homework checks
Count sig figs and round answers the way your teacher expects.
Engineering
Avoid implying more precision than a measurement really has.
Scientific notation
Write large and small numbers so their precision is clear.
Round to decimal places or place values with the rounding calculator, convert to and from powers of ten with the scientific notation calculator, and check lab results with the percent error calculator.
Sig fig calculator FAQ
What are significant figures?
They are the digits in a number that carry meaningful information about its precision, starting from the first non-zero digit.
Are trailing zeros significant?
Only when there is a decimal point. 2.50 has three significant figures, but 250 has two unless it is written as 250. or 2.50 × 10².
Are leading zeros significant?
No. In 0.0072 the zeros only show the decimal position, so there are two significant figures.
How many sig figs does 100 have?
One, by the usual convention, because the trailing zeros have no decimal point. Write 100. or 1.00 × 10² for three.
How do I round to 3 significant figures?
Keep the first three significant digits and round based on the fourth. 0.0045678 becomes 0.00457.
Why do I need to type the number as text?
Trailing zeros like those in 2.500 matter for sig figs, and a normal number box would drop them. Typing the number exactly keeps every digit.