Solve
Type the number exactly as you wrote it down: the zeros you typed are part of the data.
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Quick guide
Understand the calculation
Type a number the way you wrote it down and the tool says how many significant figures it carries, marking which zeros count and which only place the decimal point. It keeps your text as written, because 1.20, 1200 and 1.200e3 do not report the same precision even though a spreadsheet collapses them to the same value. Give it an N as well and it returns the same number rounded to that many figures.
When to use this tool
Use it to check how many figures a measurement actually reports before copying it into a write-up; to decide how many figures a result should be written with; to see why an integer ending in zeros carries no definite precision and how to write it unambiguously; or to round to N figures without a spreadsheet's binary rounding deciding an exact half for you. It does no arithmetic between measurements: uncertainty propagation and the statistics calculators cover that.
How the count and the rounding work
Every digit written from the first non-zero one onward counts. Leading zeros only place the decimal point and do not count; zeros trapped between other digits always count; trailing zeros written after the decimal point count too, because they are not needed to place the point and nobody writes them without having measured them. The exception is an integer coefficient without a decimal point: in both 1200 and 1200e3, the trailing zeros may be measured digits or placeholders. The exponent changes the scale but does not settle that question. The tool reports the conventional reading — trailing zeros do not count — with the full range and unambiguous alternatives. Rounding works on the decimal you wrote rather than on its binary approximation: it rounds to the nearest value and, when the discarded part is exactly half, to the even digit. That is why 92.85 to three figures gives 92.8, and 1.005 to three figures gives 1.00. When the fixed form of the result would be ambiguous again — 1200 to three figures — it is written in scientific notation, the form the NIST SI guide recommends for stating precision beyond doubt.
Significant figures report the resolution of a value; they do not replace a stated uncertainty. This tool reads one number at a time and does not operate between measurements: the addition rule, decided by the last decimal place in common, and the multiplication rule, decided by the smallest figure count, belong to a calculation with several operands. There is no rounding-policy selector either: some courses round every exact half up, while this utility always breaks ties to the even digit. Input limits are 50 written digits, exponents between −100 and 100, and N from 1 to 20.
How to write 1200 unambiguously
- 1200 · integer with no decimal point
2 by convention; could be 3 or 4 - 1.2e3 · two significant figures
1.2 × 10³ = 1200 - 1.20e3 · three significant figures
1.20 × 10³ = 1200 - 1.200e3 · four significant figures
1.200 × 10³ = 1200 - 1200. · four significant figures
the trailing point declares the zeros measured
Frequently asked questions
How many significant figures does 1200 have?
By convention it counts as 2, because trailing zeros in an integer do not count unless they are declared measured. But the writing alone does not settle it: it could be 2, 3 or 4. If you measured them, write it as 1.200e3 or as 1200.; if they only set the magnitude, 1.2e3 says exactly that.
Does the trailing zero in 1.20 count?
Yes. A zero written after the decimal point is not needed to place the point, so it reads as a measured figure. 1.2 and 1.20 report different precisions.
How many significant figures does zero have?
There is no universal count. A written zero states how far the measurement went — 0.00 reaches the hundredths — but it has no first non-zero digit, which is also why it cannot be rounded to N significant figures.
Why does 92.85 rounded to three figures give 92.8 and not 92.9?
Because the discarded part is exactly half and the tie goes to the even digit. Always rounding that case up biases a long series of data toward higher values.
Does this calculator do arithmetic with significant figures?
No. It reads and rewrites one number at a time. Adding or multiplying measurements applies two different rules — the last decimal place and the smallest figure count — and that is not what this utility solves.