Significant Figures Calculator
Enter a number and how many significant figures to keep, and the calculator rounds it correctly — showing the rounding place so you can see exactly which digit decides the result.
Any precision
Round to one, three, or ten significant figures — the calculator finds the leading digit and rounds at the right place every time.
Count from the first non-zero digit
Leading zeros never count as significant; the first significant figure is always the first non-zero digit you meet.
What are significant figures?
The digits that carry real precision
Significant figures are the digits in a number that actually carry meaning about its precision. Counting starts at the first non-zero digit and continues through every digit after it. Rounding to a chosen number of significant figures keeps the precision you can defend and trims digits that only look exact — essential in science, engineering, and statistics.
Enter a number and a target count to round it to that many significant figures, with the rounding step shown.
Find the place value of the leading digit, shift the number so the last significant figure sits in the units place, round to a whole number, then shift back.
rounded = round(value × 10^(sig figs − d)) ÷ 10^(sig figs − d)Here d is the number of digits to the left of the leading position, d = floor(log₁₀|value|) + 1. For 1234.56, d = 4, so to keep 3 significant figures you scale by 10^(3 − 4) = 10⁻¹, round 123.456 to 123, and scale back to 1230. The same routine gives 0.0042 → 0.004 at one significant figure and 3.14159 → 3.142 at four.
The rounded value shows only the digits you chose to trust. A measurement reported to 3 significant figures, like 1230, claims accuracy to roughly the nearest ten — the trailing zero here is a placeholder, not a guaranteed exact digit. Fewer significant figures means a coarser, more cautious figure; more significant figures claim higher precision, which you should only keep if your measurement actually supports it. A common rule when multiplying or dividing is that the answer carries as many significant figures as the least precise input, so rounding at the end avoids overstating accuracy. Watch out for trailing zeros in whole numbers: 1230 could mean 3 or 4 significant figures depending on context, which is exactly why scientists often prefer scientific notation to make the count unambiguous.
Rounding is a presentation step, not a correction.
Round once, at the end
Round only the final answer. Rounding intermediate steps and then carrying those rounded numbers forward introduces error that compounds. This tool uses round-half-up, while some scientific conventions use round-half-to-even (banker's rounding), so a value sitting exactly on a 5 may differ by one in the last place. The result reflects the digits you keep, not any new measurement accuracy.