Great question — this is one of those details that’s easy to overlook until you’re trying to get leaves and dirt out from under a heavy bench. In most outdoor furniture specifications, the typical clearance height under an outdoor bench for sweeping is around 6 to 12 inches, or about 15 to 30 cm. A minimum of about 6 inches is commonly cited because it allows a standard broom head or a small rake to pass underneath, while 10 to 12 inches is even better for quick, comfortable sweeping or using a leaf blower.
If you’re measuring, take the distance from the ground to the lowest horizontal member under the seat, such as a lower rail, stretcher, or seat slat edge. Benches with less than 4 inches of clearance tend to trap debris and become a headache to clean. For most public and residential outdoor benches, I’d aim for at least 6 inches, and if the design allows, 10 to 12 inches is a maintenance-friendly sweet spot.