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Significant Figures Calculator

Count the significant figures in any number with a digit-by-digit explanation, or round a number to a target number of significant figures in plain and scientific notation.

Works with negatives, decimals, and scientific notation such as 6.022e23. Calculated in your browser, nothing is uploaded.

Significant figures
4
Which digits counted
0.004500
  • Leading zeros never count, no matter how many there are.
  • A zero between two significant digits always counts.
  • Trailing zeros count only when a decimal point is shown.

How to count or round to significant figures

  1. Pick a mode

    Choose Count significant figures to analyze a number, or Round to significant figures to round one to a target precision.

  2. Type the number

    Enter any number, including negatives, decimals, or scientific notation such as 6.022e23. The result updates as you type.

  3. Set a target, if rounding

    In round mode, also enter how many significant figures you want the result to have.

  4. Read or copy the result

    See the significant figure count with a digit-by-digit explanation, or the rounded value in plain and scientific notation, then copy it.

Why use this tool

Digit-by-digit explanation

Every digit in the number you type is marked as significant or not, with a plain reason: leading zero, captive zero, or trailing zero with or without a decimal point.

Rounds to any target precision

Round a number to between 1 and 20 significant figures and see the result in both plain and scientific notation at once.

Handles scientific notation both ways

Type a number already in scientific notation such as 6.022e23, and get scientific notation back out for a rounded result, with the exponent kept separate from the digit count.

No floating-point precision loss

Rounding works from the digits you typed rather than converting through an ordinary number, so very large and very small magnitudes stay accurate.

Runs entirely in your browser

Every calculation happens on your device as you type. Nothing is uploaded.

About this tool

Significant figures are the digits in a number that carry real meaning about its precision, and the rules for which digits count are easy to misremember. This tool applies them for you: leading zeros never count, a zero sitting between two non-zero digits always counts, and a trailing zero counts only when a decimal point is shown, since a bare trailing zero without one is ambiguous. Type any number, including a negative, a decimal, or scientific notation such as 6.022e23, and the count mode marks every digit with the reason it did or did not count.

The round mode takes the same kind of input plus a target number of significant figures, and returns the rounded value in both plain notation and scientific notation. Rounding works directly from the digits you typed instead of converting through an ordinary floating point number first, so a very large figure such as a distance in kilometres or a very small one such as a concentration in moles keeps its precision instead of drifting from rounding error. For turning a fraction into a decimal or checking a related conversion, the scientific notation converter and the percentage calculator work alongside this tool.

Significant figures come up most often in chemistry, physics, and any lab measurement where a result should not claim more precision than the instrument that produced it. Everything here runs on the page as you type, and the numbers you enter are never uploaded, stored, or logged.

Frequently asked questions

What counts as a significant figure?
Every non-zero digit is significant. A zero between two significant digits is significant. Leading zeros, the ones before the first non-zero digit, never count. Trailing zeros count only when the number has a decimal point; without one, a trailing zero is ambiguous and treated as not significant.
Why does a decimal point change whether a zero counts?
Writing a trailing zero after a decimal point, or showing a decimal point at the end of a whole number such as 100., is a deliberate way of stating that the zero was measured rather than just a placeholder. Without the decimal point, 100 could mean the value was only measured to one or two significant figures, so the trailing zeros are left uncounted.
How are significant figures counted in scientific notation?
Only the digits in the coefficient count; the exponent is never part of the significant figure count. For example, 5.00 times 10 to the 3rd has three significant figures because of the coefficient 5.00, regardless of the size of the exponent.
How does rounding to significant figures work?
The tool finds the first significant digit in the number, keeps as many digits after it as the target count, and rounds the following digit up or down using standard rounding. It works directly on the digits you typed rather than through ordinary floating point arithmetic, which keeps very large or very small numbers accurate.
What happens with an all-zero number like 0.00?
A value of exactly zero is a special case with no universally agreed rule, since there is no non-zero digit to anchor the count. This tool treats it as one significant figure by convention rather than guessing at a specific precision.
Is my data uploaded anywhere?
No. Every number you type is processed in your browser and never sent to a server, stored, or logged.

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