√18 ≈ 4.2426
√18 is an irrational number, so its decimals never end or repeat. It sits between 4 and 5 because 4² = 16 and 5² = 25.
| Decimal places | Value |
|---|---|
| 0 | 4 |
| 1 | 4.2 |
| 2 | 4.24 |
| 3 | 4.243 |
| 4 | 4.2426 |
| 5 | 4.24264 |
| 10 (digits) | 4.2426406871 |
18 = 9 × 2 and √9 = 3, so √18 = 3√2.
4.2426 × 4.2426 ≈ 17.9997, which is very close to 18.
Need another number? Use the square root calculator (also cube roots and other roots).
| Number | Square root |
|---|---|
| 14 | 3.7417 |
| 15 | 3.8730 |
| 16 | 4 |
| 17 | 4.1231 |
| 19 | 4.3589 |
| 20 | 4.4721 |
| 21 | 4.5826 |
| 22 | 4.6904 |