Significant figures describe the meaningful written digits of a measurement or stated value.
Use them to report calculations without pretending the result is more precise than the inputs justify.
The key rule
What stays true
12.30 × 4.5 = 55.35 → 55
See the idea
Visual explanation
12345retain two significant figures → 55
Example
Apply it
Multiplication keeps the smaller significant-figure count.
Significant-figure rules are reporting conventions, not a full uncertainty analysis.
Quick guide
How to use this calculator
Enter two written values; use a decimal marker or scientific notation to clarify trailing zeros.
Choose +, −, ×, or ÷.
Compare the exact intermediate with the conventionally reported value.
Calculation method
Reporting rules depend on the operation
Addition and subtraction retain the coarser last-significant place. Multiplication and division retain the smaller significant-figure count. Half-even resolves an exact rounding tie.
Worked example
Multiplication with stated precision
12.30 has four significant figures and 4.5 has two, so the exact product 55.35 is reported with two significant figures.
12.30 × 4.5 = 55.35 → 55
Supported inputs
Precision and limits
Exact decimal input
Finite decimals use integer-scaled arithmetic, with no binary floating-point conversion.
Input boundary
Unless stated otherwise, use at most 200 digits total and 100 digits after the decimal marker.
Not uncertainty analysis
These are written-digit reporting conventions; they do not estimate experimental uncertainty.
