1. **Problem:** Evaluate $\sqrt{64}$. 2. **Formula used:** The square root of a number is the value that, when multiplied by itself, gives the original number. 3. **Apply the rule:** We want the number $x$ such that $x^2=64$. 4. **Check the value:** $8^2=8\times 8=64$. 5. **Final answer:** $\sqrt{64}=8$.