Rounding Decimals

Rounding decimals uses the same rules as rounding whole numbers — you just apply them to decimal places instead.

The Rounding Rules

1. Find the digit in the rounding place
2. Look at the digit one place to its right (the “decision digit”)
3. If the decision digit is 5 or more, round up (add 1 to the rounding digit)
4. If the decision digit is 4 or less, round down (keep the rounding digit as-is)
5. Drop all digits to the right of the rounding place

Rounding to the Nearest Tenth

Example 1: Round 3.847 to the nearest tenth

• Tenths digit: 8
• Decision digit (hundredths): 4
• $4 < 5$ → round down

$3.847 \approx 3.8$

Example 2: Round 12.65 to the nearest tenth

• Tenths digit: 6
• Decision digit: 5
• $5 \geq 5$ → round up

$12.65 \approx 12.7$

Rounding to the Nearest Hundredth

Example 3: Round 0.4872 to the nearest hundredth

• Hundredths digit: 8
• Decision digit (thousandths): 7
• $7 \geq 5$ → round up

$0.4872 \approx 0.49$

Example 4: Round 5.6039 to the nearest hundredth

• Hundredths digit: 0
• Decision digit: 3
• $3 < 5$ → round down

$5.6039 \approx 5.60$

Note: The trailing zero in $5.60$ matters — it shows precision to the hundredths place.

Rounding to the Nearest Whole Number

Example 5: Round 7.491 to the nearest whole number

• Ones digit: 7
• Decision digit (tenths): 4
• $4 < 5$ → round down

$7.491 \approx 7$

Example 6: Round 3.96 to the nearest whole number

• Ones digit: 3
• Decision digit: 9
• $9 \geq 5$ → round up

$3.96 \approx 4$

Rounding with Carrying

Sometimes rounding up causes a chain reaction, just like carrying in addition.

Example 7: Round 9.97 to the nearest tenth

• Tenths digit: 9
• Decision digit: 7
• $7 \geq 5$ → round up, but $9 + 1 = 10$, so carry: tenths becomes 0, ones goes from 9 to 10, carry again

$9.97 \approx 10.0$

Summary Table

When Rounding Matters

Match your rounding to the context. More decimal places is not always better — it can imply false precision.

Practice Problems

Test your understanding with these problems. Click to reveal each answer.

Key Takeaways

• The rounding rule is the same for decimals as for whole numbers: 5 or more rounds up, 4 or less rounds down
• Drop all digits to the right of the rounding place after rounding
• Rounding up can cause carrying ($9.97 \to 10.0$)
• Trailing zeros after rounding show precision — $5.60$ is not the same as $5.6$ in measurement contexts
• Match rounding precision to the context (money, measurement, etc.)

Return to Arithmetic for more foundational math topics.