Rounding Numbers Calculator
Round a number to a chosen number of decimal places using round-half-up, round up, round down or round to nearest.
How it works
Rounded = round(value × 10ᵖ) ÷ 10ᵖ, where p = decimal places (round replaced by ceil / floor / trunc for other modes)
Rounding shortens a number to a set number of decimal places by scaling it up, applying a whole-number rule, and scaling back down. "Nearest" rounds to whichever value is closer, breaking ties by rounding half up. Ceiling always rounds toward positive infinity, floor toward negative infinity, and truncation simply drops the extra digits toward zero.
Worked example
3.14159 rounded to 2 decimal places: multiply by 100 to get 314.159, round to the nearest whole number 314, then divide by 100 for 3.14.
Frequently asked questions
What is round half up?
When the digit being dropped is exactly 5, the last kept digit is rounded up. So 2.5 rounds to 3 and 2.45 rounds to 2.5 at one decimal place.
What is the difference between floor and truncate?
For positive numbers they match, but for negatives they differ: floor(-2.3) is -3 (toward negative infinity) while truncating -2.3 gives -2 (toward zero).
How is this different from significant figures?
Decimal-place rounding fixes the number of digits after the point; significant-figure rounding counts meaningful digits from the first non-zero digit, regardless of the decimal point.
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This calculator is for educational purposes. Double-check important results before acting on them.