Significant Figures Calculator
Round a number to a chosen number of significant figures.
Results update as you type.
How it works
Significant figures are the digits in a number that carry real, reliable information about its precision, starting from the first non-zero digit. This significant figures calculator rounds any value to the number of significant figures you choose, which is a routine requirement in science, engineering, and any field that reports measurements. The rules can be fiddly by hand: leading zeros never count, non-zero digits always count, zeros between non-zero digits count, and trailing zeros count only when a decimal point is present. When you round 3.14159 to three significant figures you get 3.14, and when you round 12345 to two you get 12000, because only the first two digits are kept as significant while the rest become placeholders. Reporting a measurement with the right number of significant figures communicates how precise your instrument was and prevents you from implying more accuracy than you actually have. Scientists use it when recording lab data, engineers when specifying tolerances, and students throughout chemistry and physics. Enter your number and the desired count, and the calculator returns the correctly rounded value without you having to track the place values manually.
round(value × 10^(n − d)) / 10^(n − d), where d = ⌈log₁₀|value|⌉
To round to n significant figures, the calculator first finds how many digits sit before the decimal point of the number's magnitude using the base-ten logarithm, then scales the number so that the last significant digit lands in the units place. It rounds to the nearest whole number there and scales back. This keeps exactly n meaningful digits, counting from the first non-zero digit, and correctly handles both very large and very small values.
Source:Standard significant-figure rounding rules
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter number and significant figures.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Rounded value updates instantly as you type — no button to press.
Frequently asked questions
What are significant figures?
Significant figures are the digits of a number that convey meaningful precision, beginning at the first non-zero digit and continuing through the last reliable digit. They tell a reader how accurately a quantity was measured. In 0.00456 there are three significant figures, the four, five, and six, because the leading zeros only position the decimal point and carry no precision information.
Which zeros are significant?
Zeros between non-zero digits are always significant, as in 1002, which has four. Leading zeros are never significant; they only locate the decimal point, as in 0.0025 with two significant figures. Trailing zeros count only when a decimal point is shown, so 2500 is ambiguous but 2500.0 clearly has five. This calculator applies these standard conventions automatically.
How do I round to significant figures?
Identify the first significant digit, count forward to the number of figures you want, then look at the next digit to decide whether to round up or down. Digits beyond your chosen count are dropped or replaced with placeholder zeros. The calculator does this for you: enter the number and how many significant figures you need, and it returns the correctly rounded result.
Why do significant figures matter?
They communicate the precision of a measurement honestly. Reporting a length as 4.5 metres implies you measured to the nearest tenth, while 4.500 claims accuracy to the nearest thousandth. Using too many figures overstates your certainty, and using too few discards real information. In science and engineering, matching the figures to the instrument's precision is a basic standard of good practice.
What is the difference from decimal places?
Decimal places count digits after the decimal point regardless of the leading zeros, while significant figures count meaningful digits starting from the first non-zero one wherever it sits. The number 0.00456 has five decimal places but only three significant figures. Significant figures track precision consistently across very large and very small numbers, which is why science prefers them.