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Significant Figures Calculator

Count significant figures in any number and round to the precision you need, with the rule applied shown every time. Built for students and lab work. Free, instant.

Significant figures

Count sig figs, or round a number to N of them.

Scientific notation like 3.20e5 is accepted.
Result

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The sig fig rules

All non-zero digits are significant. Zeros between significant digits count, leading zeros never do, and trailing zeros count only when a decimal point is present: 0.0045070 has five sig figs, while 45070 without a decimal is ambiguous.

The tool applies these rules and tells you which one decided the count, so it doubles as a study aid.

Rounding to N sig figs

Switch to round mode, set N, and the number is rounded with standard half-up rounding to exactly N significant figures. This is the step students need after multiplying or dividing measurements, where the answer cannot be more precise than the least precise input.

Scientific notation input like 3.20e5 is accepted and keeps its trailing-zero meaning.

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Sig Figs Calculator FAQs

How many significant figures does 0.0045070 have?
Five: 4, 5, 0, 7 and the trailing 0. Leading zeros are never significant; they only place the decimal point. Trailing zeros after a decimal point always count.
Why are trailing zeros ambiguous without a decimal point?
In 45070 it is unclear whether the final zero was measured or just fills place value. This tool does not count it; write 4.5070e4 in scientific notation to make trailing zeros significant unambiguously.
How do I round 0.0045678 to 3 significant figures?
Pick round mode, enter the number and N=3. The result is 0.00457: the first three significant digits 4, 5, 6, with the 7 rounding the 6 up.
Do exact numbers like 1000 have 1 or 4 sig figs?
Written plainly, 1000 is ambiguous and this tool counts 1. If all four digits are significant, write 1000. with a decimal point or 1.000e3.
Is this useful for lab reports?
Yes. It is built for exactly that: counting sig figs in measurements and rounding calculation results so your reported precision never exceeds what you measured.
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