T-Rex vs Other Dinosaurs: Size Comparison for Kids

T-Rex vs Other Dinosaurs: Size Comparison for Kids

When most kids think of dinosaurs, they think of Tyrannosaurus rex — the terrifying, tiny-armed predator that has starred in countless movies and books. But was T-Rex really the biggest, most fearsome dinosaur of all time? The answer might surprise you. Let's put T-Rex up against some of its prehistoric rivals in the ultimate dinosaur size comparison!

First, How Big Was T-Rex?

• Length: Up to 12–13 metres (about the length of a bus)
• Height: Around 4 metres at the hip
• Weight: Up to 8,000–9,000 kg (heavier than an African elephant)
• Bite force: The most powerful of any land animal ever — around 35,000–57,000 Newtons
• Teeth: Up to 30 cm long, shaped like bananas

The Biggest Dinosaurs Ever

Argentinosaurus — The Heavyweight Champion

Argentinosaurus is believed to be the largest dinosaur ever discovered. This plant-eating sauropod from South America was estimated to be:

• Length: 30–40 metres (three times longer than T-Rex!)
• Weight: Up to 70,000–80,000 kg — nearly 10 times heavier than T-Rex

Spinosaurus — Longer Than T-Rex

Spinosaurus was actually longer than T-Rex, reaching up to 14–18 metres. It had a distinctive sail on its back and was semi-aquatic, hunting fish in rivers and swamps. Recent research suggests Spinosaurus may have been the largest carnivorous dinosaur ever.

Brachiosaurus — The Tall One

• Height: Up to 13 metres tall (taller than a four-storey building)
• Length: Around 26 metres
• Weight: Around 56,000 kg

Ankylosaurus — The Tank

Ankylosaurus wasn't the longest or tallest, but it was built like an armoured tank. Its body was covered in bony plates and spikes, and its tail ended in a massive club that could shatter bone. Even T-Rex would have thought twice before attacking an Ankylosaurus.

The Smallest Dinosaurs

• Microraptor: About the size of a crow, with four wings, it could glide between trees.
• Compsognathus: About the size of a chicken, it was one of the smallest known dinosaurs.
• Anchiornis: Roughly the size of a pigeon, it's one of the earliest known bird-like dinosaurs.

T-Rex's Surprising Weaknesses

• Its arms were tiny — only about 1 metre long, too short to reach its own mouth.
• It had poor forward vision compared to modern predators (though recent research suggests its vision may have been better than previously thought).
• It was likely not a fast runner — estimates suggest a top speed of around 17–25 km/h.
• It may have been partly a scavenger, eating animals that were already dead.

Dinosaur Size Activities for Kids

• Measure it out: Use chalk on a driveway or tape on a floor to mark out the lengths of different dinosaurs.
• Weight comparison: Research how many kids it would take to equal the weight of a T-Rex or Argentinosaurus.
• Design your dinosaur: If you could create a new dinosaur, what size would it be? What would it eat? Draw and describe it.
• Dinosaur debate: Which dinosaur would win in a fight — T-Rex or Ankylosaurus? Debate the evidence!

Build Your Dinosaur Collection

Our Hidden Valley collection features beautifully crafted wooden dinosaur figurines, from the mighty T-Rex to plant-eating giants, made from sustainably sourced timber.

Shop the Hidden Valley Collection →

Further Reading & Resources

These trusted museums, research institutions, and educational sites are fantastic for exploring dinosaur science further:

• Natural History Museum — Dino Directory — the London Natural History Museum's comprehensive dinosaur database, with detailed profiles of hundreds of species including size comparisons, diet, and discovery history. Perfect for research.
• National Geographic — Prehistoric Animals — stunning photography, videos, and up-to-date facts about dinosaurs and other prehistoric creatures, ideal for curious kids and classroom projects.
• American Museum of Natural History — Dinosaurs — one of the world's greatest natural history museums shares its dinosaur research, exhibitions, and educational resources online.
• DK Find Out — Dinosaurs — child-friendly, curriculum-aligned dinosaur facts with interactive content and size comparisons, perfect for primary school learners.
• Australian Age of Dinosaurs — Australia's own dinosaur museum in Winton, Queensland, dedicated to Australian dinosaur discoveries — including some of the largest dinosaurs ever found in the Southern Hemisphere.

Explore more on our Ramblings blog — including what Stegosaurus ate and how we know about dinosaurs through fossils.