Rounding Calculator

What is Rounding Calculator?

Type a number, choose round/round-up/round-down, and how many decimal places, and get the result instantly. Useful for currency, measurements, or any calculation that needs a specific precision. A quick way to double-check how a value should round before hardcoding that logic in code, or to settle a disagreement about whether a price or measurement should round up or down at a given decimal place. Calculation happens live in your browser as you type.

How to Use the Rounding Calculator

1. 1

   Enter a Number: Type the value you want to round.

2. 2

   Choose a Mode and Precision: Pick round, round up, or round down, and the number of decimal places.

3. 3

   Read the Result Instantly: The rounded value appears automatically.

The Three Rounding Modes

This tool shifts your number by the chosen number of decimal places (multiplying by 10^places), applies one of three JavaScript rounding functions, then shifts back:

• Round: Uses standard round-half-up (JavaScript's Math.round). A value exactly halfway rounds toward positive infinity, so 2.5 rounds to 3, but -2.5 rounds to -2 (not -3), since "up" here means toward positive infinity rather than away from zero.

• Round up (ceiling): Always moves to the next representable value in the positive direction, even for negative numbers: -1.5 rounds up to -1, not -2.

• Round down (floor): Always moves toward negative infinity: -1.5 rounds down to -2.

How to Round a Number

Worked example: 3.14159 to 2 decimal places. Round: 3.14159 × 100 = 314.159 → rounds to 314 → 314 / 100 = 3.14 Round up: 314.159 → ceiling gives 315 → 3.15 Round down: 314.159 → floor gives 314 → 3.14 A worth-knowing edge case: because decimals like 1.005 can't be represented exactly in binary floating point, rounding 1.005 to 2 decimal places with standard "round" gives 1, not 1.01. That's a quirk of how JavaScript (and most languages) store decimal numbers, not a bug in the rounding logic itself.