Decimal rounding is a fundamental mathematical operation used to simplify numbers by reducing the number of digits after the decimal point. This is essential in many fields, including finance, science, engineering, and everyday calculations, to ensure clarity, manage precision, and adhere to specific reporting standards.
The process involves looking at the digit immediately to the right of the last digit you want to keep.
If this digit is 5 or greater, you round up the last kept digit (increase it by one).
If this digit is less than 5, you keep the last kept digit as it is (round down).
Any digits to the right of the rounding position are discarded.
For example, rounding 123.45678 to two decimal places:
The number is 123.45678.
We want to keep 2 decimal places, so we look at the first two digits after the decimal: .45.
The next digit (the third decimal place) is 6.
Since 6 is greater than or equal to 5, we round up the last kept digit (5) to 6.
The rounded number is 123.46.
Rounding to zero decimal places means rounding to the nearest whole number. For example, rounding 123.45678 to 0 decimal places:
The number is 123.45678.
We want to keep 0 decimal places, so we look at the digit immediately after the decimal point, which is 4.
Since 4 is less than 5, we keep the last digit before the decimal point (3) as it is.
The rounded number is 123.
This calculator automates this process, allowing you to quickly and accurately round any number to a specified number of decimal places.
function roundDecimal() {
var decimalValueInput = document.getElementById("decimalValue");
var decimalPlacesInput = document.getElementById("decimalPlaces");
var resultDisplay = document.getElementById("result");
var valueStr = decimalValueInput.value.trim();
var placesStr = decimalPlacesInput.value.trim();
// Clear previous result if inputs are empty
if (valueStr === "" || placesStr === "") {
resultDisplay.textContent = "–";
return;
}
var value = parseFloat(valueStr);
var places = parseInt(placesStr, 10);
// Validate inputs
if (isNaN(value)) {
resultDisplay.textContent = "Invalid Number";
return;
}
if (isNaN(places) || places < 0) {
resultDisplay.textContent = "Invalid Decimal Places";
return;
}
// Perform rounding using toFixed and then converting back to Number to remove trailing zeros
// Note: toFixed returns a string. We use parseFloat to convert it back.
var roundedValue = parseFloat(value.toFixed(places));
// Check if the result is a valid number after rounding
if (isNaN(roundedValue)) {
resultDisplay.textContent = "Error in rounding";
} else {
resultDisplay.textContent = roundedValue.toString();
}
}