Rounding Calculator

A rounding calculator turns a decimal number into a simpler value — but there is more than one way to do it. This tool applies four methods at once, round, floor, ceil, and truncate, and shows the results side by side at any precision from 0 to 15 decimal places, so you can see exactly how each rule behaves on the same number.

The four methods: round() goes to the nearest value, floor() always goes down, ceil() always goes up, and trunc() simply drops the digits beyond your chosen precision.

The Four Methods on 3.7

round(3.7) = 4

Goes to the nearest whole number.

floor(3.7) = 3

Always rounds down toward −∞.

ceil(3.7) = 4

Always rounds up toward +∞.

trunc(3.7) = 3

Cuts off the decimal part.

How to Round a Number

Enter a Decimal Number

Type any value you want to round — positive or negative, with as many decimals as you like.

Set the Decimal Places

Choose a precision from 0 (whole numbers) up to 15 digits. Use 1 place for the nearest tenth or 2 for the nearest hundredth — every method rounds to that many places.

Compare All Four Results

round, floor, ceil, and trunc appear together so you can instantly see where they agree and where they differ.

Adjust and Watch It Update

Every result recalculates live as you change the number or the precision — there is no button to press.

Watch the negatives: floor and truncate differ for negative inputs. floor(−3.7) = −4 (toward −∞) but trunc(−3.7) = −3 (toward 0).

Features

Four Methods at Once

round, floor, ceil, and trunc computed together on one number for easy comparison.

Custom Precision

Pick any decimal precision from 0 to 15 digits for whole numbers or fine detail.

Side-by-Side View

See all four results together to choose the right rule for your task.

Instant Live Results

Numbers update the moment you type — no submit button needed.

Private by design: every calculation runs in your browser. Nothing you type is uploaded, and the tool works offline once the page has loaded.

Rounding 3.7 Compared

Method	Result	Behavior
round(3.7)	4	Nearest integer
floor(3.7)	3	Down toward −∞
ceil(3.7)	4	Up toward +∞
trunc(3.7)	3	Drops decimals
round(−3.7)	−4	Nearest integer
floor(−3.7)	−4	Down toward −∞

Frequently Asked Questions

What is the difference between floor and truncate?

For positive numbers they are identical. For negative numbers they differ: floor(−3.7) = −4 because floor always moves toward −∞, while trunc(−3.7) = −3 because truncate simply removes the decimal part, moving toward zero.

How do I round to the nearest tenth or hundredth?

Set the decimal places field to control the place value. Use 1 for the nearest tenth (one digit after the point), 2 for the nearest hundredth, 3 for the nearest thousandth, and so on up to 15.

Which rounding method should I use?

Use round() for general-purpose rounding, floor() when you must always round down (for example, how many whole items you can afford), ceil() when you must always round up (such as the number of packages required), and trunc() when you simply want to drop the decimals.

How is an exact half like 2.5 rounded?

round() rounds halves up toward positive infinity, so 2.5 becomes 3 and 3.5 becomes 4. For a negative half the same rule applies toward +∞, so −2.5 becomes −2.

How many decimal places can I set?

Any precision from 0 to 15 decimal places. Set it to 0 to round to whole numbers, or increase it for high-precision results in scientific and financial work.

Do these methods work on negative numbers?

Yes. All four methods accept negative inputs. Just remember that floor moves toward −∞ while ceil moves toward +∞ and trunc moves toward zero — which is exactly why the side-by-side comparison is so useful.