Significant Figures Calculator
Significant Figures Calculator round to sig figs measurement digit rounder significant digit answerRound by meaningful digit count
Enter one finite decimal or E-notation value, choose 1 through 15 significant figures, and select Round number. Standard and scientific displays show the same rounded magnitude.
Which zeros count
Leading zeros before the first nonzero digit do not count. Zeros between nonzero digits do count. Trailing zeros after a decimal point can communicate precision, which is why scientific output preserves them. For zero itself, this calculator returns zero rather than claiming the input established measured precision.
How rounding works
The tool retains the requested leading significant digits and uses the next digit to round the last retained one. A next digit of five or more rounds upward. A carry can change magnitude: 9.99 rounded to two figures becomes 10, displayed scientifically as 1.0 × 10¹.
Worked example
Enter 0.004567 and choose three significant figures. Leading zeros are placeholders, so the significant digits are 4, 5, 6, and 7. The next digit is 7, which rounds 6 upward. The result is 0.00457, or 4.57 × 10⁻³.
Standard versus scientific display
Scientific notation makes trailing precision explicit and avoids long runs of zeros. Standard form is expanded when practical. For very large or tiny values, it may use E notation because JavaScript and browsers cannot present an unlimited decimal string safely.
Supported limits and assumptions
Input accepts a sign, decimal point, and optional e exponent. Expressions, commas, units, infinity, and values outside JavaScript's finite number range are rejected. Arithmetic uses binary floating-point, so decimal boundary cases can reflect representation limits. The tool rounds a number; it cannot infer measurement uncertainty or how many original digits were trustworthy.
Significant Figures FAQ
Is this the same as decimal places?
No. Decimal places count positions after the decimal; significant figures begin at the first nonzero digit.
Why show scientific notation?
It exposes requested trailing zeros without ambiguity.
Does 1200 have two or four significant figures?
The text alone can be ambiguous. Context or scientific notation must state intended precision.