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Comparison of a brachiosaurus and a person

Comparison of a brachiosaurus and a person (dottedhippo, iStockphoto)

How Large Were Dinosaurs?

Digital Development Team
Text,  Images
Biology,  Science


Students develop their observation and comparing and contrasting skills as they explore the size of dinosaurs.


Students explore the size of dinosaurs by measuring out the length of a Tyrannosaurus in the classroom, and then compare and contrast its size to that of the classroom, model dinosaurs, other types of dinosaurs and themselves.


30-45 minutes

Setting the Stage

More than 1 000 species of dinosaur are known from fossil evidence, ranging in size from small bird-like dinosaurs that were less than 1 m (~3’) to huge long-necked sauropods that reached lengths of 40 m (~130’) or more. Some dinosaurs (including all meat-eating dinosaurs) walked on two legs. The rest walked on four legs. Some ate plants, others ate meat. Many dinosaurs had humps, plates or spikes on various parts of their bodies. Some dinosaurs had feathers covering parts of their bodies, while others had scales.

Did you know? 

The largest known dinosaur is believed to be Argentinosaurus. That’s a long-necked sauropod that scientists believe could reach a length of 40 m (130’) and a mass of up to 100 tonnes (100 tons). It is likely that dinosaurs even larger than Argentinosaurus lived, but not enough fossil bones have been found to make a reliable estimate. Only a few bones (usually vertebrae) have been found of these animals.

Fossil bones provide clues about the size and shape of extinct animals 

The skeletons of dinosaurs are the best indicators we have as to their sizes and shapes. Aside from the bones themselves, markings on the bones can show where muscles and tendons were attached. This can help palaeontologists to ‘flesh out’ the animal. But skeletons do not tell the whole picture of what an animal looks like. The skeletons of some animals, such as whales, look very different from the live animals, and it would be difficult to accurately determine their shape just by looking at their skeletons.

This inquiry provides opportunities for students to develop their observation and comparing and contrasting skills as they explore the size of dinosaurs. It is recommended that students have completed the What is a Dinosaur? inquiry before doing this inquiry. 

As students examine dinosaur models and measure out the length of a life-sized Tyrannosaurus rex they will be able to compare the actual size of a dinosaur with the size of their classroom, their own size, as well as other familiar objects. This opportunity for comparison will help students develop an understanding of the size and scale of dinosaurs. By extending this learning task to examine the size of other types of dinosaurs, students will gain an appreciation for the diversity of these extinct creates that once roamed the Earth.

This inquiry could begin from:

  • observations and comments about the size of toy dinosaurs. Discuss using questions such as:
    • How big do you think this living dinosaur was? 
    • If we compare these models of dinosaurs, how do we know which dinosaur was bigger? 
    • Why do we often use models to observe and discuss dinosaurs?
    • How do we know how big dinosaurs really were? What evidence do we have about their size?
Scale models of dinosaurs
Scale models of dinosaurs (©2019 Let’s Talk Science).
  • a discussion about the ways that we can measure and compare living things. Discuss using questions such as: 
    • What are some different ways that we can compare living things? (e.g., colour, size, weight, body features, behaviours, foods eaten, etc.)
    • When you go to the doctor for an examination, what measurements of you does the doctor make? Why?
    • What measurements are always taken when a baby is born? Why is the weight of a baby is very important to take and record over the first year of life? 
    • How is the height of a horse measured? How come it is measured this way?
    • What would be an important measurement for a snake? Why?
    • What are some different ways we can compare dinosaurs? What measurements would you like to know about dinosaurs?
Child having height measured
Child having height measured (Source: FatCamera via iStockphoto).
  • discussions about dinosaur fossils and displays students have seen at a museum . Discuss using questions such as: 
    • What can a fossil of a dinosaur tell us about the size of it? What other things can be learned from fossilized bones? (e.g., markings on the bones can show where muscles and tendons were attached, the shape and position of hip bones and leg bones can indicate how they stood and moved)
    • What was the smallest dinosaur skeleton in the museum? What was the biggest skeleton?
    • How did the museum display the dinosaur fossils? Why was there not a complete skeleton for each dinosaur? 
    • What do you call a scientist who studies dinosaur bones? (Palaeontologist)
Graphic showing the relative sizes of Argentinosaurus huinculensis and a human
Graphic showing the relative sizes of Argentinosaurus huinculensis and a human (Let’s Talk Science using an image by Slate Weasel via Wikimedia Commons).


  • Toy dinosaur (Tyrannosaurus and/or any other dinosaurs which will be measured)
  • Illustration of Tyrannosaurus (optional) 
  • Rope or string, at least 15 metres (~50’) long, marked at 1 metre intervals (optional)
  • Paper for charting (optional)
Toy dinosaurs
Toy dinosaurs (©2020 Let's Talk Science)


  • Gather toy dinosaurs.
  • Prepare the rope or string by tying knots, tying ribbons or marking the rope or string with a marker at 1 metre intervals
Model Tyrannosaurus
Model Tyrannosaurus (Source: M W via Pixabay).

Did you know?

Tyrannosaurus rex was a large carnivorous dinosaur that lived approximately 65 million years ago in the western United States and Canada. The first Tyrannosaurus was discovered in 1903. Since then, several dozen have been found.

What to Do


  • Explore the toy dinosaur.
    • Educator supports and facilitates exploration. Discuss if the toy dinosaur is as large as the real dinosaur was. If measuring Tyrannosaurus, show the illustration of Tyrannosaurus and discuss the grid on the illustration.
    • Estimate how large the real dinosaur might have been. Count how many boxes long the Tyrannosaurus in the illustration is.
    • Predict whether the dinosaur would have fit in the classroom. If using a chart, record the students’ predictions.
Tyrannosaurus rex illustration on a one metre grid
Tyrannosaurus rex illustration on a one metre grid (©2019 Let’s Talk Science).
  • Measure out the length of Tyrannosaurus
    • Using a knotted rope or string, take the roll to one corner of the room. The educator invites a child to hold the end of the rope or string. Unroll the rope or string, with a child holding onto each knot (ribbon, etc.). Continue until the rope or string is as long as the full-sized dinosaur (i.e., 14 people to measure out a 13 m (~40’) long Tyrannosaurus).
    • Measuring Option: If there is no rope or string, children can stand side by side with arms outstretched so that the tips of their fingers touch. A preschool child’s arm span is approximately 1 m (3’), so continue having children stand beside each other until they have reached the length of the Tyrannosaurus (i.e., 13 children for a 13 m (~40’) long Tyrannosaurus).
    • Compare where the children are standing along the line to the toy dinosaur or dinosaur image. Ask questions such as, “Who is standing at the dinosaur’s legs, head, etc.?”, “How many students equal the length of the dinosaur’s tail?”
  • Compare the toy dinosaur to the full-sized dinosaur size measured out. 
    • Educator facilitates by asking questions such as: “How much larger is the full-sized dinosaur?”, “How many model dinosaurs would fit along the length of this rope that is the length of a Tyrannosaurus? That number is the scale of the toy dinosaur.” (e.g., 1 Tyrannosaurus length equals 50 models, which can be written as a ratio of 1:50 or 1/50)

Misconception Alert

Not all dinosaurs were huge. Like mammals or fish, dinosaurs came in a wide variety of sizes. Many dinosaurs were quite small, including tiny Compsognathus, which as an adult was about as large as a chicken, and the famous Velociraptor, which was about as tall as a typical preschool child (adult length of 1 metre [~3’]).

  • Predict - Students make predictions about the size of different dinosaurs
  • Measure - students use measuring and numeracy skills to determine the length of a dinosaur
  • Observe - students observe the length of a dinosaur, as represented as a length of measured rope
  • Compare & Contrast - students compare and contrast the length of a dinosaur with the length of their classroom, themselves and other familiar objects. Student may go further and identify similarities and differences in the sizes of different dinosaurs, based on additional measurements, observations and new and prior knowledge
Co-constructing Learning
Saying, Doing, Representing
Responding, Challenging

Students make predictions about the size of a Tyrannosaurus in relation to the size of their classroom.


  • “How big was Tyrannosaurus compared to our classroom? Do you think a Tyrannosaurus is larger or smaller than our classroom?”
  • How many Tyrannosaurus could fit in our classroom? Would we be able to put two Tyrannosaurus in this space?”
  • “How could we experience the size of Tyrannosaurus for ourselves?”
  • “What tools could we use to measure the length of a dinosaur?”
  • “How have scientists determined the size of dinosaurs?”

Students use measuring and numeracy skills to measure rope representing the length of a dinosaur and make observations. 

  • “What are we using to measure out the length of the dinosaur?”
  • “What distance do each of these knots (or ribbons or tape) represent?" (1 metre)
  • “How many metres long is the dinosaur from head to tail?”
Students compare and contrast the length of the dinosaur with the model dinosaur, the size of the room and themselves to learn about how big dinosaurs were.
  • Was this dinosaur able to fit in this room? Would this dinosaur be able to turn around in this room?” 
  • “How many of our model dinosaurs would fit along the length of the full-sized dinosaurs?” 
  • “How many students can stand shoulder to shoulder along the length of this dinosaur?”
  • “How would you feel if you were standing beside this dinosaur?”
Cross-curricular Connections


  • Use oral language to explore and develop an understanding of ideas and concepts (e.g., the difference between small and large, short and long; understanding the concept of scale)
  • Use processing skills (e.g., draw conclusions about the relative size of specific dinosaurs and familiar spaces)

Mathematical Thinking

  • Organize objects into categories by sorting and classifying objects (e.g., sort and classify toy dinosaurs and toy animals by size and scale)
  • Ordering (e.g., arranging toy dinosaurs by size, from shortest to longest and shortest to tallest)

Visual Arts

  • Drawing and fine-motor skills (e.g., by tracing the outlines of dinosaur models or templates)
  • Making a scale drawing of their favourite dinosaur, using grid paper and basic dimensions, like length.
  • Collaborate on creating a mural of a life-sized dinosaur. (e.g., by using an overhead projector to expand an image of a dinosaur to life-size)
Enfant peinture avec un dinosaure
Child painting with a dinosaur (Source: BrianAJackson via iStockphoto).
Extending the Learning
  • Measure out the length of other species of dinosaurs with the rope. Refer to the Dinosaur Length Chart for dinosaur sizes. Just from looking at the dinosaur names, students could predict which dinosaur is longest.
  • Read a book such as Dinosaurs Big and SmallGigantic! How Big were the Dinosaurs? or Prehistoric Actual Size. Discuss using questions such as: 
    • What types of things were the big dinosaurs compared to in the book? What were the small dinosaurs compared to?
    • What have we learned about the sizes of dinosaurs? 
    • What are some examples of small dinosaurs? Do you think small dinosaurs would be less dangerous than the big dinosaurs? Why or why not? 
  • Compare the size of various dinosaurs to living animals (e.g., cows, hawks, elephants, whales, etc.) and human-made objects (e.g., buildings, cars, trucks, etc.).

Dinosaur Length Chart

Name Type/Description Length
Compsognathus Small meat-eating dinosaur 0.8 m (~2 ½’)
Gallimimus Bird-like dinosaur 4 m (~13’)
Centrosaurus Ceratopsian (horned dinosaur) 6 m (~20’)
Albertosaurus Large meat-eater 8 m (~26’)
Stegosaurus Plated dinosaur 9 m (~30’)
Ankylosaurus Armoured dinosaur 10 m (~33’)
Parasaurolophus Duckbill with large crest on head 10 m (~33’)
Tyrannosaurus One of largest known meat-eaters 13 m (~40’)
Brachiosaurus Large sauropod; 13 m (~40’) tall 23 m (~75’)
Diplodocus Large sauropod, among longest dinosaurs known 30 m (~100’)
Supporting Media


Tyrannosaurus rex Illustration [Google Doc] [PDF]

Scaled drawing of Tyrannosaurus


Cover of Dinosaurs Big and Small by Kathleen Weidner Zoehfel
Cover of Dinosaurs Big and Small by Kathleen Weidner Zoehfeld (Source: Open Library).

Dinosaurs Big and Small

By Kathleen Weidner Zoehfeld

Illustrated book describing and comparing dinosaurs of different sizes. 

ISBN: 9780064451826

Cover of Gigantic! How Big were the Dinosaurs? by Patrick O’Brien
Cover of Gigantic! How Big were the Dinosaurs? by Patrick O’Brien (Source: Open Library).

Gigantic! How Big were the Dinosaurs?

By Patrick O’Brien

Gigantic! puts some of children's favorite dinosaurs head-to-head with monster trucks, cherry pickers, and tanks.

ISBN: 9780805057386

Cover of Prehistoric Actual Size by Steve Jenkins
Cover of Prehistoric Actual Size by Steve Jenkins (Source: Open Library).

Prehistoric Actual Size

By Steve Jenkins

What is it like to come face-to-face with the ten-foot-tall terror bird? Or stare into the mouth of the largest meat eater ever to walk the earth? Can you imagine a millipede that is more than six feet long, or a dinosaur smaller than a chicken? In this “actual size” look at the prehistoric world, you’ll meet these awe-inspiring creatures, as well as many others.

ISBN: 9780544582385

Learn More

Jordan Mallon - Research Scientist in Palaeobiology (Careers)

Career profile of a Research Scientist in Palaeobiology.