Significant Figures Calculator
Round any number to a specified number of significant figures. Also counts the significant figures in any number and converts to scientific notation.
Rules for Significant Figures
- Non-zero digits are always significant: 123 has 3 sig figs
- Zeros between non-zeros are significant: 1002 has 4 sig figs
- Leading zeros are NOT significant: 0.0056 has 2 sig figs
- Trailing zeros after decimal ARE significant: 1.500 has 4 sig figs
- Trailing zeros without decimal are ambiguous: 1200 could have 2, 3, or 4
Frequently Asked Questions
Significant figures communicate the precision of a measurement. Reporting more digits than your measurement allows implies false precision. In scientific calculations, your answer should have no more sig figs than your least precise input.
What significant figures represent
Significant figures record how precisely something was measured. Writing 2.5 cm claims precision to the nearest millimetre; writing 2.500 cm claims precision ten times finer. They are not the same statement, even though the numbers are equal.
Counting rules
- Non-zero digits always count. 472 has 3.
- Zeros between non-zeros count. 4072 has 4.
- Leading zeros never count. 0.0036 has 2 — they only mark the decimal position.
- Trailing zeros after a decimal point count. 3.200 has 4.
- Trailing zeros in a whole number are ambiguous. 1500 could be 2, 3 or 4. Scientific notation removes the doubt: 1.5 × 10³ is clearly 2.
Multiplying and dividing
The result carries as many significant figures as the least precise input.
Example: 4.56 × 2.1
The raw answer is 9.576, but 2.1 has only 2 significant figures, so the result is 9.6.
Adding and subtracting
Different rule — here you match decimal places, not significant figures.
Example: 12.52 + 3.1
Raw total 15.62, but 3.1 has one decimal place, so the answer is 15.6.
Applying the multiplication rule to addition is a very common mistake. Keep them separate.
Why it matters
Reporting more digits than your measurement supports overstates what you know. If you time a race with a stopwatch reading to 0.1 s, writing 12.4738 s implies precision your equipment never had.
The reverse is just as bad: rounding too hard throws away real information and compounds through a calculation.
Practical advice
Carry extra digits through intermediate steps and round only at the end. Rounding at every stage accumulates error — in a long chain that drift can become larger than the figure you're trying to report.
Exact counted values, like 12 items or 100 cm in a metre, have infinite significant figures and never limit a result.