How significant figures calculator works
Significant figures (sig figs) are the digits in a number that carry meaningful precision — everything a measurement or calculation can actually support. Four rules cover counting: all non-zero digits are significant; zeros between non-zero digits are significant; leading zeros (0.00103) are never significant; and trailing zeros are significant only when the number contains a decimal point. So 1200 has 2 significant figures, 1200. has 4, and 10.0 has 3.
This tool counts the significant figures in any number you type and, if you give it a target, rounds the number to that many significant figures. The input is treated as text on purpose: typing 0.0010300 preserves the trailing zeros that a plain numeric field would silently strip, and scientific notation like 1.20e3 keeps its three significant figures in the mantissa. The count follows the standard rules above, including the convention that a written zero such as 0.00 counts by its decimal places.
Rounding works from the leftmost significant digit: 1234 to 3 significant figures is 1230, and 9999 to 3 is 10000 — a result that can gain a digit, which is why the tool also shows the scientific-notation form (1.00 × 10^4) that states the precision unambiguously. Where the plain decimal result would need more than 100 decimal places or the value is very large, the scientific form becomes the primary output.