A standard two-axle bus has six wheels. It typically uses two wheels on the front axle and four wheels on the rear axle, arranged as dual wheels on each side.
The extra rear wheels help support the bus's considerable weight and improve traction. The rear axle is usually the driven axle, while the front axle steers. This arrangement is common on full-size transit, school, and intercity buses.
The word “wheels” can cause confusion because people sometimes count axles instead. A two-axle bus has two axles, but that does not mean it has four wheels. Likewise, a bus with three axles may have six or more wheels, depending on whether its axles use single or dual tires.
Smaller buses and minibuses can differ: some use single rear wheels, while articulated buses often have three axles or more. For the conventional full-size two-axle design intended by this question, six is the standard count.