How to Round Numbers (and Significant Figures)

Rounding numbers makes them easier to read, share, and work with, but doing it wrong can introduce errors that add up. Knowing how to round numbers correctly, and understanding decimal places versus significant figures, is a small skill with a big payoff in everyday maths, money, and measurements. The core rule is simple: look at the next digit and decide whether to round up or down. This guide explains that rule clearly, works through examples for both decimal places and significant figures, and covers the tie-breaking case of a digit exactly on 5. For related calculations, our percentage calculator handles the numbers for you.

The basic rounding rule

Every rounding task follows the same simple rule:

1. Decide the place you are rounding to, such as the nearest whole number or two decimal places.
2. Look at the digit immediately to the right of that place.
3. If that digit is 5 or more, round up (increase the last kept digit by one). If it is less than 5, round down (leave the last kept digit unchanged).
4. Drop the digits after your rounding place.

Rounding to decimal places

Decimal places count the digits after the decimal point. To round to two decimal places, you keep two digits after the point and look at the third to decide.

• 3.14159 to 2 decimal places: the third digit is 1 (less than 5), so it rounds down to 3.14.
• 3.146 to 2 decimal places: the third digit is 6 (5 or more), so it rounds up to 3.15.
• 2.5 to the nearest whole number: the next digit is 5, so it rounds up to 3.

Significant figures

Significant figures count meaningful digits starting from the first non-zero digit. They are useful when the scale of a number matters more than its decimal places, common in science and measurements.

• 3.14159 to 3 significant figures: the first three significant digits are 3, 1, 4, and the next digit is 1, so it stays 3.14.
• 2,847 to 2 significant figures: the first two are 2 and 8, and the next digit is 4, so it rounds to 2,800.

Leading zeros are never significant, so in 0.0056 the significant figures start at the 5.

Let a calculator handle precision

Our percentage calculator and unit converter give precise results you can round as needed. Rounding at the end, rather than mid-calculation, keeps your answers accurate.

The exactly-5 case

When the digit is exactly 5 with nothing meaningful after it, the standard school rule is to round half up, so 2.5 becomes 3 and 0.45 becomes 0.5. This is the most common convention and the one most people expect.

Some fields use bankers rounding, which rounds a half to the nearest even number to reduce bias over many calculations, so 2.5 becomes 2 and 3.5 becomes 4. Unless you are told otherwise, round half up.

Why rounding matters

Rounding makes numbers clearer, a price of 19.99 is easier than 19.9873, but it also introduces small errors. The key habit is to round only at the final step, not partway through a calculation, because rounding early and then continuing can compound the error. Carry full precision through your working, and round the final answer to a sensible number of places for your context.

Frequently asked questions

How do I round numbers?

Look at the digit immediately after the place you are rounding to. If it is 5 or more, round up by increasing the last kept digit by one; if it is less than 5, leave the last kept digit as it is. Then drop the following digits. For example, 3.14159 rounded to two decimal places is 3.14.

How do I round to two decimal places?

Keep two digits after the decimal point and look at the third digit. If it is 5 or more, round the second digit up; if less than 5, leave it. So 3.146 rounds up to 3.15, while 3.142 rounds down to 3.14. Rounding to two decimal places is common for money and everyday figures.

What is the difference between decimal places and significant figures?

Decimal places count digits after the decimal point, while significant figures count meaningful digits starting from the first non-zero digit anywhere in the number. For 0.0056, there are four decimal places but only two significant figures. Decimal places suit money and fixed precision; significant figures suit science, where scale matters.

How do I round when the digit is exactly 5?

The standard rule is to round half up, so a trailing 5 rounds the previous digit up: 2.5 becomes 3 and 0.45 becomes 0.5. Some technical fields use bankers rounding, which rounds a half to the nearest even number to reduce bias, but round half up is the usual, expected convention.

Should I round during a calculation or at the end?

Round only at the end. Rounding partway through and then continuing can compound small errors into a noticeably wrong final answer. Carry the full precision through every step of your calculation, and round the final result to a sensible number of decimal places or significant figures for your situation.

The bottom line

To round a number, check the digit after your chosen place: 5 or more rounds up, less than 5 rounds down. So 3.14159 becomes 3.14 to two decimal places, and 2,847 becomes 2,800 to two significant figures. Use decimal places for money and significant figures for scientific precision, round a trailing 5 upward by default, and always round at the very end. For precise results to round, use our percentage calculator.

Further reading

For authoritative background on this topic, see Rounding on Wikipedia.