Is there a simple formula for determining alcohol content without consulting a table?

All you need to determine alcohol content is the original or starting gravity and the final gravity. Just drop the decimal points, subtract the smaller one from the bigger, and divide by 7.5. For example, If your starting gravity is 1.055, and your final gravity is 1.010, you would have 1.055 - 1.010 = 45 divided by 7.5 = 6% alcohol.