Did you know that a standard beach towel is 30 inches by 60 inches? That sounds like a lot, but it's actually only barely bigger than a normal bath towel. Because of how beach towels are used, it's much better to have a towel that's a little bigger than standard.
A beach towel should be long and wide enough to lie on, but not so big that it's unwieldy. With the average human height ranging from 62 to 67 inches, a beach towel should be at least 70 inches long. 35 inches wide is a good minimum and lets most people lie comfortably, without having to pin their arms to their sides to avoid sand.
Sometimes you'll pay a good deal more for towels labeled "oversized," since standard beach towels don't actually work for a standard human. Try to find a seller like Hencely, one with a wide selection of beach towels that are all long enough to be truly comfortable, whether you're lying down in the sun or wrapping yourself up in the soft cotton.