The tsunami's propagation took 5 hours to reach Western Australia, 7 hours to reach the Arabian Peninsula, and did not reach the South African coast until nearly 11 hours after the earthquake.

The sudden vertical rise of the seabed by several metres during the earthquake displaced massive volumes of water, resulting in a tsunami that struck the coasts of the Indian Ocean. A tsunami that causes damage far away from its source is sometimes called a teletsunami and is much more likely to be produced by vertical motion of the seabed than by horizontal motion.

The tsunami, like all others, behaved differently in deep water than in shallow water. In deep ocean water, tsunami waves form only a low, broad hump, barely noticeable and harmless, which generally travels at a high speed of 500 to 1,000 km/h (310 to 620 mph); in shallow water near coastlines, a tsunami slows down to only tens of kilometres per hour but, in doing so, forms large destructive waves. Scientists investigating the damage in Aceh found evidence that the wave reached a height of 24 metres (80 ft) when coming ashore along large stretches of the coastline, rising to 30 metres (100 ft) in some areas when traveling inland. Radar satellites recorded the heights of tsunami waves in deep water: maximum height was at 600 millimetres (2 ft) two hours after the earthquake, the first such observations ever made.

According to Tad Murty, vice-president of the Tsunami
 Society, the total energy of the tsunami waves was equivalent to about 5 megatons of TNT (21 PJ), which is more than twice the total explosive energy used during all of World War II (including the two atomic bombs) but still a couple of orders of magnitude  less than the energy released in the earthquake itself. In many places the waves reached as far as 2 km (1.2 mi) inland.

Because the 1,600 km (1,000 mi) fault affected by the earthquake was in a nearly north-south orientation, the greatest strength of the tsunami waves was in an east-west direction. Bangladesh, which lies at the northern end of the Bay of Bengal, had few casualties despite being a low-lying country relatively near the epicenter. It also benefited from the fact that the earthquake proceeded more slowly in the northern rupture zone, greatly reducing the energy of the water displacements in that region. 

Maximum height of the waves that hit Indonesia

Coasts that have a landmass between them and the tsunami's location of origin are usually safe; however, tsunami waves can sometimes diffract around such landmasses. Thus, the state of Kerala was hit by the tsunami despite being on the western coast of India, and the western coast of Sri Lanka suffered substantial impacts. Distance alone was no guarantee of safety, as Somalia was hit harder than Bangladesh despite being much farther away. 
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