20 inches

How Tall Are Bmx Bikes? Rider Height Rider Age (Avg.) Top Tube Length 4′ 5′′ to 4′ 10′′ 8 to 10 18′′ to 18.5′′ 4′ 5′′ to 5′ 2′′ 10 to 13 19′′ to 19.5′′ 4′ 8′′ to 5′ 5′′ 10 to 13 19.5′′ to 20′′ 5′ 6′′ to 5′ 10′′ 13 & over 20.5′′