Rounding Calculator – Decimals & Whole Numbers

Rounding replaces a number with the closest value at a chosen precision. To round 3.14159 to two decimals, inspect the third decimal (1): since it is below 5, the result is 3.14. Ties are where methods split: half-up sends 2.5 to 3, while banker’s rounding (half-to-even) sends 2.5 to 2 and 3.5 to 4 to avoid systematic upward bias across large data sets — the default in Python’s round(). Whole-number places work the same: 145 to the nearest ten examines the ones digit (5) and rounds to 150 under half-up. The calculator supports decimals, tens, hundreds, thousands, and a significant-figures mode (0.003409 → 0.00341 at 3 sf). It also shows the rounding error, e.g. 145 → 150 adds +5, and the interval of numbers that share your rounded result.

1. 1

   Enter your number

   Type any decimal like 3.14159 or 2456.78

2. 2

   Choose the target place

   Decimal places, tens, hundreds, thousands or significant figures

3. 3

   Pick a tie rule

   Half-up (school default) or half-to-even (banker’s rounding)

4. 4

   Round and inspect

   See the result, the error introduced, and the rounding interval

• 1

  The deciding digit is one place to the right of your target

• 2

  0.5 ties: half-up always rounds up; half-even alternates to reduce bias

• 3

  Rounding twice is lossy: 2.349 → 2.35 → 2.4, but direct rounding gives 2.3

• Rounding sequentially (2.349 → 2.35 → 2.4) instead of in one step to 2.3

• Assuming 2.5 always rounds to 2 in banker’s rounding only contexts, or vice versa

• Confusing decimal places with significant figures for numbers like 0.00340

• Rounding before finishing intermediate calculations and compounding error