Giant Clam Size Comparison: Just How Big Do They Get?

Key Points 

• There are 12 species of giant clams 
• Tridacna gigas is the largest of the giant clam species 
• Giant clams are not dangerous; humans pose a greater risk to the clam than the clam does to us. 
• Other giants in the ocean are the giant octopus and giant manta rays.

The first clam-like species existed nearly 252 million years ago. Giant clams (Tridacna gigas) are the largest living bivalve mollusks. These clams feature thick, heavy shells with soft tissue on the inside. Both their shells and tissue inside boast a variety of beautiful colors and patterns. There are 12 known species of giant clams. These mollusks are found in the Indian and South Pacific Oceans and are often found in reef flats and shallow sandy areas of lagoons about 65 feet deep.

After attaching themselves to coral, these mollusks stay there for their entire lives. That means they do not go out and actively hunt for food; instead, they hunt using their siphoning system. They take in the water and filter their prey — like zooplankton — out of it. Just how big is the giant clam? That is what we aim to answer! This article will discuss the giant clam’s size in isolation and compare it with other ocean wildlife. 

Types of Clams and Their Sizes 

An adult giant clam will range between 4 and 4.5 feet long and weigh about 500 pounds. They have large, heavy mantles, which account for about ten percent of their body weight. These large mollusks are usually found in depths of about 65 feet since shallow waters allow them access to sunlight. While the giant clam is the biggest, there are 12 species of giant clams, all larger than those you may see on your dinner plate. The six largest clams are listed below:

• Gigas clam — also know as giant clam — (Tridacna gigas) 
• Fluted giant clam (Tridacna squamosa) 
• Small giant clam (Tridacna maxima) 
• Southern giant clam (Tridacna derasa) 
• Bear Paw clam (Hippopus hippopus) 
• Boring clam (Tridacna crocea) 

All of these clams are at least 12 inches long, much different than the one- to two-inch clams on your plate! Below is a table that shows the size difference between the giant clam, the other six largest clams, and two of the traditionally eaten smaller clams. 

Giant Clam vs. Human Size Comparison

Humans may come into contact with giant clams if they dive into the ocean. Many giant clams call The Great Barrier Reef their home, and this is a popular diving spot for many people. Humans may be fascinated by the giant clam’s beautiful colors and large size. The clam is an average size of 4 feet, which is similar to the average-sized human. 

The average human male is around 5 feet and 6 inches tall, and the average human female is around 5 feet and 2 inches tall. That means the average human is only about one foot larger than the giant clam! Hold up a ruler; that is how much larger a giant clam is to your average human. The average weight of an adult human male — in America, because it differs based on continent — is about 199 pounds, and the average weight for an adult human female — also in America — is around 163 pounds. This weight is significantly less than the giant clam’s average of 500 pounds. 

While close in length, humans are no match for the weight of the giant clam. The clam more than doubles a human’s average weight. 

Giant Clam vs. Giant Octopus Size Comparison 

Another ocean giant that is found near coral reefs is a distant relative of the clam; it is the giant octopus (Enteroctopus dofleini). The octopus is a cephalopod, which is a group of swimming mollusks. Believe it or not, the octopus has a shell, too; however, its shell has been reduced to two small plates on its head where its head muscles anchor. This giant can be found across the Pacific Ocean, ranging in habitat from Japan to Alaska. 

These two giants are likely to encounter one another in the wild because although the giant octopus can dive to depths of 4,900 feet, it can also be found in shallow water like its cousin. The giant octopus would be a hard creature to miss as the largest octopus species. Although its body is only about 2 feet long, its arm span is an average of 7 feet long, and it can easily reach up to 13 feet long. Even though these creatures are much larger, a full-grown giant octopus only weighs about 50 pounds. The largest giant octopus measured about 20 feet across and weighed over 200 pounds. 

Although the giant octopus is much longer than the giant clams because of its arm span, it is much lighter. 

Giant Clam vs. Giant Manta Ray Size Comparison 

Another giant in the ocean is the giant manta ray (Manta birostris). These rays are the largest of their species and are found worldwide. Similar to giant clams, giant manta rays are filter feeders, and zooplankton is one of their main food sources. These rays are slow-growing and have a lifespan of about 45 years. They can be found sharing habitats with the giant clam because when they feed, they prefer shallow waters; however, they are known to dive up to 3,000 feet. 

Easily recognizable from their diamond-shaped bodies and “wings” — their pectoral fins — these rays have a wingspan of up to 30 feet. They also have an impressive weight of up to 5,300 pounds! These giants give the giant clam a run for their money in the size department, seeing as they are both longer and heavier than the giant mollusks! 

Giant Clam vs. Leatherback Sea Turtle 

Leatherback sea turtles (Dermochelys coriacea) are the largest sea turtles in the world. They get their name from their unique shell that differs from other turtles’ shells. Most turtles have a hard outer shell, but the leatherback sea turtle’s shell is made up of thin, rubber-like skin. The leatherback sea turtle can be found all over the world. Their habitat ranges from venturing onto land during mating season to diving to ocean depths of up to 4,000 feet. 

Leatherback sea turtles average around 7-8 feet in length and can weigh up to 2,000 pounds. They are about half the size of a Volkswagen Beetle Type 1! The largest leatherback sea turtle ever recorded weighed 2,120 pounds and measured 9 feet and 5.5 inches long. This is the largest sea turtle, and this giant is bigger than the giant clam, too! Coming in at 8 feet, this turtle is about double the clam’s size and more than double its weight! 

Giant Glam vs. Inshore Fishing Boat Size Comparison 

Giant clams are often found in shallow waters and among coral reefs. Those shallow waters can be tricky for fishermen to access with large boats, but inshore fishing boats are perfect. Inshore fishing boats can reach shallow, hard-to-reach locations that larger boats could not access. 

The average inshore fishing boat ranges between 17-20 feet long. The 177 sports model — an inshore fishing boat — is 17 feet and 7 inches long and weighs 1,000 pounds. It can hold 545 pounds inside of it. While the giant clam is much smaller than this boat — only 4 feet long — it is interesting that this boat would only be able to hold one of the giant clams because of its weight. Regardless, the giant clam is no match for the size and weight of the inshore fishing boat; the boat is 4-5 giant clam lengths. 

How Big Are Giant Clams When They Are Born? 

Although these clams are significant in size as adults, they are not born giants. Each giant clam has both sperm and eggs, and it reproduces by releasing both into the water. The eggs are fertilized by the sperm released by another giant clam — this is called broadcast spawning. The fertilized eggs then hatch into larvae. 

Clam larvae are less than 0.1mm — or 0.0039 inches — long, about the width of a human hair. When the larvae settle, they reach about 0.2mm — or 0.008 inches — long. It takes years for the giant clam to get its adult weight and size, but seeing as it can live to be 100 years old, it is in no rush! 

The Largest Giant Clam Ever Recorded 

There are over 15,000 species of clam, and North America has the greatest variety of clams. The largest clam ever recorded was a giant clam. It was found in Indonesia and was 510 pounds and 4.49 feet long. It was said that had the clam been found alive, it would have weighed closer to 550 pounds. Currently, that clam can be found in a museum in Northern Ireland. 

Giant clams — like other clams — are capable of producing pearls. What’s the difference? Due to their immense size, the giant clam’s pearls weigh up to 75 pounds and have a value of 100 million dollars! 

Is a Giant Clam Bigger Than a Great White Shark?

The great white shark (Carcharodon carharias) is the largest predatory fish species in the world. Great white sharks are one of the most potent predators with a fearsome reputation, accounting for half of the annual shark attacks on humans. These ocean giants have been around for nearly 20 million years. Great whites are widely distributed worldwide but are most commonly found in temperate and tropical coastal regions, cooler waters, and the open ocean. Known to travel great distances, a great white would likely pass by a giant clam in one of its migrations or hunting expeditions. 

These sharks are known to grow up to 26 feet long and weigh over 2 tons — 4,000 pounds. That is dramatically bigger than the giant clam. Coming in at only 4 feet long, it would take almost seven giant clams to equal the length of one great white shark! The shark is also eight times the weight of the clam. With that being said, the giant clam is not bigger than the great white shark. 

Where Do Giant Clams Live? 

Giant clams can be found in the Indian and South Pacific Oceans. They live in reef flats and shallow sandy areas of lagoons at about 65 feet deep. They like the shallow waters because it allows them access to sunlight, which they capture by opening their shell and allowing the sunlight to filter through the clear spots on their mantle. The sunlight helps with the photosynthesis of the algae that usually reside in the clam’s tissue. 

Many giant clams are found on The Great Barrier Reef. The giant clam is considered a sessile animal, meaning it lives in one place its entire life. Once the clam attaches to a section of the reef, it stays there for life. 

Other Common Giant Clam Questions

Why do giant clams get so big?

Giant clams get so big because they receive “additional nourishment from symbiotic photosynthetic bacteria.” These clams have a mutually beneficial relationship with algae because while the algae is protected inside the clam’s body, the clam gets additional nutrients, allowing it to grow bigger. 

How long does it take a clam to become a giant? 

Giant clams live to be about 100 years old and are slow-growing. At five years old, they are about 3 feet and don’t reach 4 feet until they are nearly ten. 

Are giant clams dangerous?

Although rumored to be “man-eating,” giant clams are not dangerous to humans. They are filter feeders and are not interested in humans. Even if the clam was interested in attacking a human — which it is not — its shell moves too slowly to trap divers. There has never been a recorded incident of a giant clam harming a human. 

Humans pose a greater risk to giant clams than they do to us. Constantly seized as a dining delicacy or for home decor, these clams are regularly victims of overfishing; this excludes the damage done to the ocean through pollution. 

Are giant clams edible? 

Giant clams are edible. The Waikik Aquarium states, “Both the clam’s mantle tissue and the large muscle that closes the shells are edible and highly prized by people throughout the Pacific and Asia.” While you can eat this clam, it does not mean you should. The giant clam is currently protected under the Endangered Species Act, and eating it goes against that act. To save the species, eating it and fishing for it — for any purpose — should be avoided. 

The photo featured at the top of this post is © Sergius Bleicher/Shutterstock.com