Significant Figures Calculator

How it works

1. 1Enter the number you want to round in the Number field.
2. 2Set how many significant figures you need (1–15).
3. 3The result updates instantly, showing the rounded value and an explanation of the rounding step.

Use cases

• Chemistry and physics students rounding measured values to match instrument precision.
• Engineers expressing results to the number of significant figures required by a specification.
• Anyone checking whether a reported number has been rounded correctly in scientific work.

Frequently asked questions

What counts as a significant figure?

All non-zero digits are significant. Zeros between non-zero digits are significant. Leading zeros (the 0s in 0.0042) are not — they only mark place value. Trailing zeros after a decimal point (2.500) are significant because they show measured precision.

How does the rounding work?

The calculator finds the digit at the chosen significant position, then looks at the next digit. If it is ≥ 5 the kept digit rounds up; otherwise it stays. Remaining digits become zero or are dropped.

Why does 0.004200 to 2 sig figs give 0.0042?

Leading zeros are not significant, so the first two significant digits are 4 and 2. Rounding to 2 sig figs keeps 4 and 2 and drops the rest, giving 0.0042.