Rounding and Significant Figures Calculator
Enter a number and choose decimal places or significant figures. The table shows the result under every common rounding rule, and the page counts the significant figures in what you typed.
Trailing zeros in a whole number such as 1200 are not counted as significant, because they may only mark the size. Write 1200. to show they are.
Worked examples
Two decimal places
2.675 to 2 decimal places
2.68
The 5 after the 7 rounds the 7 up to 8.
Significant figures
123,456 to 3 significant figures
123,000
The fourth figure is 4, so the third figure stays as 3.
About Rounding and Significant Figures Calculator
Rounding swaps a number for a nearby, simpler one. The school rule is to look at the first digit you are dropping: 5 or more rounds up, and less than 5 rounds down. This calculator rounds to a set number of decimal places, to the nearest ten, hundred or thousand by using a negative number of places, or to a number of significant figures. A table underneath shows the result under every common rule side by side, so you can see exactly where the rules differ.
It works on the digits you actually typed rather than on a stored approximation, which matters. Many programs turn 2.675 into 2.67 when rounding to two places because the stored value is slightly under 2.675, while the school rule gives 2.68. Here you get 2.68. The page also counts the significant figures in what you typed, following the standard rules: leading zeros never count, zeros between other digits always count, and zeros after the decimal point count when they follow a digit.
How to use Rounding and Significant Figures Calculator
- Choose whether to round to decimal places or to significant figures.
- Type the number you want to round.
- Enter the number of places or figures. Use a negative number of places, such as -1, to round to tens.
- Pick a rounding rule and read the result, or compare every rule in the table.
Common uses
- Rounding exam answers to the requested accuracy
- Reporting measurements with the right number of significant figures
- Rounding money to the nearest penny or pound
- Seeing how banker's rounding differs from the school rule
Frequently asked questions
How many significant figures does 0.004560 have?
Four: 4, 5, 6 and the final zero. The zeros before the 4 only show where the decimal point is, but the zero at the end counts because it comes after the decimal point and follows other digits.
What is banker's rounding?
It is rounding half to even. A number exactly halfway goes to the nearest even digit, so 2.5 becomes 2 and 3.5 becomes 4. Over many numbers it avoids a steady upward drift.
How do I round to the nearest hundred?
Choose decimal places and enter -2. Rounding 1,234.5 to -2 places gives 1,200.
Are the zeros at the end of 1200 significant?
Not by the usual rule, because they may only show the size of the number. Writing 1200. with a point, or 1.200 × 10^3, shows that they are.
Do negative numbers round differently?
Under the half up rule, the page rounds halves away from zero, so -2.5 becomes -3. The up and down rules in the table differ for negative numbers, so check the rule you need.