Rounding Calculator

What this calculator does

This calculator applies a single rounding rule to a single number. It supports five methods and the most common targets — decimal places (tenths through ten-thousandths), whole numbers, and powers of ten (10, 100, 1000) — plus a custom decimal-places field.

Formula

To a step s: result = round(value ÷ s) × s

To n decimals: equivalent to step s = 10⁻ⁿ.

Methods: half-up (away from 0 on .5), truncate (toward 0), floor (toward −∞), ceiling (toward +∞), banker's (half to even).

Variable definitions

• value — The number you want to round.
• s — The step or place value you round to.
• n — Decimal places when rounding to a decimal target.

Step-by-step calculation

1. Divide the value by the chosen step.
2. Apply the rounding method to the quotient.
3. Multiply back by the step to return to the original scale.
4. Report the rounded value and the signed difference from the original.

Worked example

Round 3.14159 to hundredths with half-up:

3.14159 ÷ 0.01 = 314.159 → 314 → 314 × 0.01 = 3.14 (difference −0.00159).

Round −2.5 to the nearest integer: half-up → −3, banker's → −2, floor → −3, ceiling → −2, truncate → −2.

How to use this calculator

1. Enter the number you want to round.
2. Pick a target — a decimal place, whole number, ten, hundred, or custom decimals.
3. Pick a method. Half-up is the default and matches most school and consumer use.
4. Copy or share the rounded result with the method and target.

Common mistakes

• Confusing floor with truncate on negatives: floor(−3.2) = −4, truncate(−3.2) = −3.
• Expecting half-up everywhere: spreadsheets and many languages default to banker's rounding. Pick the method that matches your downstream tool.
• Double rounding: rounding twice (first to four decimals, then to two) can give a different answer than rounding once to two decimals. Round once, at the final step.

Frequently asked questions