Rounding and estimating
When do you round up, and when down? And how do you quickly see whether an answer is reasonable? Try it yourself.
The explanation is shown. Quick: the common roundings. Advanced: also thousands and significant figures — and the number rounded every way.
Your numbers
Answer
Rounded to hundreds
3,500
How to work it out
- 1Look at the digit right after: 8
- 2It is 5 or more — round up.
- 33,486.749 ≈ 3,500
The formula
0, 1, 2, 3, 4 → down · 5, 6, 7, 8, 9 → up
The rounding rule: the digit right after decides.
Estimate: round first, calculate afterwards
An estimate tells you whether the answer is reasonable — e.g. whether 48 · 21 is close to 1,000.
In depth: more numbers and “what if”
3,486.749 rounded every way
| Round to | Result |
|---|---|
| hundredths | 3,486.75 |
| tenths | 3,486.7 |
| whole numbers | 3,487 |
| tens | 3,490 |
| hundreds | 3,500 |
| thousands | 3,000 |
| 1 significant figures | 3,000 |
| 2 significant figures | 3,500 |
| 3 significant figures | 3,490 |
| 4 significant figures | 3,487 |
More: Numbers and percentages
- PercentPercentage of, how many per cent, percentage change, discount and VAT.
- FractionsAdd, subtract, multiply and divide fractions — and simplify the answer.
- Powers and rootsPowers, square roots, nth roots and numbers as powers of 10.
- Primes and divisorsIs it a prime? Prime factors, divisors, GCD and LCM.
- Order of operationsEnter a calculation and see it worked out step by step in the right order.
- Number systems and Roman numeralsBinary, hexadecimal and Roman numerals — converted both ways with working.