What is first class mail postage rate from the mainland to Hawaii?

As of my last knowledge update in October 2023, the First-Class Mail postage rate for sending letters from the mainland United States to Hawaii is generally the same as for domestic mail sent within the contiguous U.S. For a standard letter (up to one ounce), the rate is typically around 66 cents. However, rates can vary based on weight and size, so it's advisable to check the latest rates on the United States Postal Service (USPS) website for the most accurate information.