Significant Figures Rounding Calculator
Round any number to a chosen number of significant figures, the way scientific and engineering work reports precision.
How it works
Round value to the first N nonzero-anchored digits: factor = 10^(N − ⌈log₁₀|value|⌉), result = round(value × factor) ÷ factor
Significant figures count the digits that carry real precision, starting from the first nonzero digit. Reporting 3.14159 to three significant figures gives 3.14, because only the first three digits are kept and the rest are rounded away. This matters in science and engineering, where the number of significant figures signals how precisely a quantity was actually measured — writing extra digits implies precision you do not have.
Worked example
3.14159 to three significant figures: the first three significant digits are 3, 1 and 4, and the next digit (1) rounds down, giving 3.14. To two figures it would round to 3.1.
Sources: Significant figures — Wikipedia
Frequently asked questions
Which digits are “significant”?
All nonzero digits count, as do zeros between them (the 0 in 102 is significant). Leading zeros never count (0.0025 has two sig figs), and trailing zeros count only when there is a decimal point (2.50 has three).
How is this different from decimal places?
Decimal places count digits after the point regardless of magnitude; significant figures count meaningful digits from the first nonzero one. 0.00456 has five decimal places but only three significant figures.
Why cap at 15 significant figures?
Standard double-precision numbers reliably hold about 15–17 significant digits. Beyond 15, rounding artifacts creep in, so the tool limits the count there.
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This calculator is for educational purposes. Double-check important results before acting on them.