The greatest stress load factor on your flagpole is WIND. Stress loading from wind is calculated by adding the load on the POLE plus the load on the FLAG flown. Creating a FLAGPOLE DESIGN that is SAFE is predicated on understanding the geographical wind stress loading to which the flagpole shall be subjected.

GEOGRAPHY is important to calculating maximum wind speed potential as a factor of flagpole selection. Consider whether the flagpole is by the COAST or INLAND, whether it is in the middle of a city or at the town's outskirts. Overall height of the flagpole also plays a factor in wind load analysis. Winds generally are higher along the coast, greater in open country than in the center of a city, and stronger as the height above ground increases.
Different size flags are APPROPRIATE for flying from different poles (height, base diameter and wall thickness). Conversely, FLAGPOLES CAN BE SPECIFIED WHICH ARE CAPABLE OF FLYING THE LARGEST FLAG DESIRED IN THE WIND ZONE TO WHICH IT WILL BE SUBJECTED.

The physics of a stress loading formula will also determine a flagpole's BUTT DIAMETER and WALL THICKNESS appropriate for flag size and wind zones.

Your FOUNDATION (ground, roof, or wall) to which a flagpole is mounted is the last design factor architects and engineers will need to determine for resistance to stress loading.