Rounding Numbers: The Rules, Method and Examples

Rounding replaces a number with a simpler one that is closest in value. The purpose is to make calculation easier and to estimate results. It is taught in Year 4 and used for life, from estimating a shopping bill to reading a financial report.

One Rule Covers Everything

The entire topic rests on a single rule:

Look at the one digit to the right of the place you are rounding to. If it is below 5, round down. If it is 5 or more, round up.

That is all. There is no separate rule for tens, hundreds or decimals — they all use the same rule, only the digit you look at changes.

Rounding to Tens, Hundreds and Thousands

To the nearest ten — look at the units digit:

• 47 → units is 7, round up → 50
• 43 → units is 3, round down → 40
• 45 → units is 5, round up → 50

To the nearest hundred — look at the tens digit:

• 380 → tens is 8, round up → 400
• 320 → tens is 2, round down → 300
• 1,250 → tens is 5, round up → 1,300

To the nearest thousand — look at the hundreds digit:

• 4,600 → hundreds is 6, round up → 5,000
• 4,400 → hundreds is 4, round down → 4,000

Rounding Decimals

The rule is identical, only you look to the right of the point. See also decimals.

To one decimal place:

• 3.47 → look at the second digit, 7, round up → 3.5
• 3.42 → look at 2, round down → 3.4

To two decimal places:

• 5.678 → look at the third digit, 8, round up → 5.68
• 5.672 → look at 2, round down → 5.67

To the nearest whole number:

• 8.7 → 9
• 8.2 → 8

Estimating a Calculation

This is what rounding is actually for, and it is what gets taught least.

Roughly what is 397 + 512?

Round to hundreds: 400 + 500 = about 900. The real answer is 909 — close enough.

Estimating is the most powerful self-checking tool a child can have. If they calculate 397 + 512 and get 1,909, they can see instantly that something is wrong without redoing the sum. That habit saves more marks than extra practice questions.

Rounding in Real Life

• Shopping: Rp 24,750 becomes Rp 25,000 for a mental total
• Change: many shops round to the nearest Rp 100
• News: "around 5 million people" is a rounded figure
• Report cards: an average of 84.67 is often written as 85

The Mistakes That Actually Cost Marks

1. Looking at more than one digit. To round 3.449 to one decimal place, look only at the first 4 after the point — the answer is 3.4. Children often see the 49 behind it and wrongly round to 3.5. This is the number one cause.

2. Rounding in stages. 3.449 → 3.45 → 3.5 is wrong. Round once, directly to the required place.

3. Thinking 5 rounds down. In school rounding, 5 always rounds up.

4. Rounding to the wrong place. Rounding to tens when hundreds were asked for. Read the question twice.

5. Truncating instead of rounding. Turning 3.47 into 3.4 by simply cutting it off. Truncating and rounding are different operations, and only rounding is being asked for.