Work out rounding numbers instantly with clear inputs, formula shown and shareable results.
Rounding to d decimal places multiplies by 10^d, rounds to the nearest whole number and divides back. Significant figures instead count from the first non-zero digit, so the place value depends on the size of the number.
Round to d places
round(v × 10^d) / 10^d
Significant figures
scale so the first significant digit is in the units place, round, then scale back
Both give 3.14 here, but for 0.00314159 two decimal places gives 0.00 while three significant figures gives 0.00314.
This uses round-half-up, so 2.5 becomes 3. Statistical work sometimes prefers round-half-to-even instead.