The three largest seashells we could find when we searched are the Giant Clam (Tridacna gigas), the Australian Trumpet (Syrinx aruanus), and the Horse Conch (Triplofusus giganteus).

1. Giant Clam (Tridacna gigas) The champion, as far as we can find, was found off Okinawa in 1956. It measured 3ft 9inches and weighed about 750lbs with the clam inside.

• Size: Up to 120 cm (4 feet) across and weighing more than 250 kg (550 lbs).
• Type: Bivalve (two shells hinged together).
• Claim to fame: The largest seashell in the world by weight and overall bulk.
• Habitat: Coral reefs of the South Pacific and Indian Oceans.
• Notes: Giant clams are living reef organisms that can survive for over a century. Their shells are so massive they’ve been compared to the size of small furniture pieces.

2. Australian Trumpet (Syrinx aruanus) This shell is huge and, suprisingly it also lives at the Bailey Mathews Museum on Sanibel Island. It was found in 1974 in Austrailia's Northwest Territory.

• Size: Up to 91 cm (3 feet) in length.
• Type: Gastropod (spiraled shell).
• Claim to fame: The largest gastropod shell in the world.
• Habitat: Northern waters of Australia, Papua New Guinea, and Indonesia.
• Notes: Its elongated spiral makes it look like a giant horn. Collectors prize it for both its rarity and sheer size.

3. Horse Conch (Triplofusus giganteus) This is the American Champion. The largest was found on Sanibel Island in 2023 and is 24 inches long. You can see it at the Bailey Mathews Museum on the island.

• Size: Up to 60 cm (2 feet) in length.
• Type: Gastropod.
• Claim to fame: The largest seashell found in U.S. waters.
• Habitat: Shallow waters of the southeastern United States, especially Florida.
• Notes: Known for its striking orange interior, the Horse Conch is iconic among shell collectors and is Florida’s official state shell.

Sumation:

• The Giant Clam wins in sheer size and weight.
• The Australian Trumpet is the longest spiraled shell ever recorded.
• The Horse Conch is the largest shell native to North America.

Together, these shells represent the extremes of mollusk growth—massive bivalves and towering gastropods that showcase the ocean’s incredible biodiversity. Maybe you know of some shells out there that are larger? If so let us know! If you are looking for large shells, we do have some at Seashell Supply. Not as large as these guys, but several that are over a foot long. Contact us or visit our site if you are interested!

Sources: Registry of World Record Size Shells, WRS Shells Database, Smore Science – Largest Seashells in the World