You enter a number and choose a place value (ones through thousandths). The tool multiplies the number by 10 raised to the precision, applies JavaScript's Math.round, Math.floor, or Math.ceil, then divides back. The difference is the absolute value of the rounded result minus the original. It uses the round-half-up convention, which is the most common rule taught in schools.
When the digit being dropped is exactly 5, round-half-up rounds the preceding digit away from zero. For example, 2.5 rounds to 3 and −2.5 rounds to −3. This is the default rule in most everyday math and accounting.
Floor is useful when you need a conservative estimate (e.g., how many full boxes fit in a space). Ceiling is useful when you need to round up to ensure coverage (e.g., how many tiles to buy so you don't run short).
Yes. In long chains of calculations, repeatedly rounding intermediate results can drift the final answer. In scientific and financial computing, it's common to carry extra decimal places through the calculation and only round the final output.
Banker's rounding (round-half-even) rounds 0.5 cases to the nearest even digit — so 2.5 rounds to 2 while 3.5 rounds to 4. This reduces cumulative bias in large data sets. This calculator uses round-half-up, not banker's rounding.
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.