Brachiosaurus feet are small in comparison to their overall size. Due to the factors of weight, ground composition and location, it is impossible to state their overall footprint size.
A typical adult brachiosaurus was 52 feet tall, and it could stretch to around 80 feet when required. Adult weight varied widely among individuals, but they were capable of weighing in excess of 50 tons.
The closest comparison to their body structure found in modern times is the giraffe. While much smaller in size, the elongated neck, leg placement and relative foot size are all similar to that of the brachiosaurus.