√66 ≈ 8.1240
√66 is an irrational number, so its decimals never end or repeat. It sits between 8 and 9 because 8² = 64 and 9² = 81.
| Decimal places | Value |
|---|---|
| 0 | 8 |
| 1 | 8.1 |
| 2 | 8.12 |
| 3 | 8.124 |
| 4 | 8.1240 |
| 5 | 8.12404 |
| 10 (digits) | 8.1240384046 |
66 has no perfect-square factor other than 1, so √66 is already in simplest radical form.
8.1240 × 8.1240 ≈ 65.9994, which is very close to 66.
Need another number? Use the square root calculator (also cube roots and other roots).
| Number | Square root |
|---|---|
| 62 | 7.8740 |
| 63 | 7.9373 |
| 64 | 8 |
| 65 | 8.0623 |
| 67 | 8.1854 |
| 68 | 8.2462 |
| 69 | 8.3066 |
| 70 | 8.3666 |