Scale Explorer

Prehistoric

How big is a Stegosaurus?

Stegosaurus · Estimated size of a large adult · Stegosaurus

Length (estimated)
≈ 9 m 30 ft approx.
Usual length (estimated)
≈ 6.5 m 21 ft approx.
Length of Stegosaurus stenops (AMNH estimate)
≈ 8.5 m 28 ft approx.
Mass (estimated)
≈ 2,720 kg 3 US tons approx.
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Human, Horse, Woolly mammoth, Stegosaurus drawn to the same scaleHuman: height 1.61–1.75 m. Horse: height at withers 1.6–1.7 m. Woolly mammoth: shoulder height (estimated) 3–3.5 m. Stegosaurus: length (estimated) ≈ 9 m.Human: 1.61–1.75 mHorse: 1.6–1.7 mWoolly mammoth: 3–3.5 mStegosaurus: ≈ 9 mStegosaurus≈ 9 mWoolly mammoth3–3.5 mHorse1.6–1.7 mHuman1.61–1.75 m
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Dimensions

MeasurementMetricImperialNotesSource
Length (estimated) ≈ 9 m ≈ 30 ft Estimated nose-to-tail length; Britannica also says some reached 9 m (30 ft). Approximate [1] [4]
Usual length (estimated) ≈ 6.5 m ≈ 21 ft Estimated: Britannica says Stegosaurus usually grew to about 6.5 m (21 ft). Approximate [4]
Length of Stegosaurus stenops (AMNH estimate) ≈ 8.5 m ≈ 28 ft Estimated; AMNH gives 8.5 meters (28 feet). Approximate [3]
Mass (estimated) ≈ 2,720 kg ≈ 3 US tons Estimated weight of Stegosaurus stenops; AMNH also gives 6,000 pounds. Approximate [3]
Mass of the NHM specimen 'Sophie' (estimated) ≈ 1,600 kg ≈ 1.8 US tons Estimated living weight of the Natural History Museum's Stegosaurus stenops, a young adult, from a 3D model of its skeleton and leg-bone measurements. Approximate [2]

About the Stegosaurus

Stegosaurus was a plant-eating armoured dinosaur that lived in North America in the Late Jurassic, about 152 to 145 million years ago. It is known for the two rows of large bony plates along its back and the spikes on its tail, and it had a very small head for its size. The Natural History Museum, London estimates it at about 9 metres long, and the American Museum of Natural History estimates about 8.5 metres and 2,720 kg for Stegosaurus stenops. These sizes are estimates, and many individuals were smaller.

  • The plates on its back were embedded in the skin rather than attached to the skeleton. O C Marsh first thought they lay flat, but a specimen held in place by mud showed they stood upright in alternating rows. [1]
  • Its brain was about the size of a plum. [1]
  • Its back legs were about twice as long as its front legs. [3]
  • Because its forelimbs were much shorter than its hind limbs, its back had a characteristic arch. [4]
  • An almost complete Stegosaurus stenops skeleton went on display at the Natural History Museum, London in December 2014. Museum scientists estimated it weighed around 1,600 kg in life, similar to a small rhino. [2]

How many fit?

  • ≈ 5.4 × Human · height lined up end to end match the Stegosaurus · length (estimated)
  • ≈ 32 × Human · body mass on the scales weigh as much as Stegosaurus · mass (estimated)
  • ≈ 7.9 × African lion · shoulder height lined up end to end match the Stegosaurus · length (estimated)
  • ≈ 12–22 × African lion · body mass on the scales weigh as much as Stegosaurus · mass (estimated)

Counts divide one sourced figure by another. "End to end" uses each object's main measurement; weight and volume rows appear only when both figures are sourced.

How it compares

  • 5.4× A Stegosaurus is about 5.4 times as long as an average adult is tall. See side by side
  • 7.9× A Stegosaurus is about 7.9 times as long as an African lion is tall at the shoulder. See side by side
  • 1.8× A Stegosaurus is about 1.8 times as long as a mid-size car. See side by side
  • 1/1.2 A school bus is about 1.2 times as long as a Stegosaurus. See side by side
  • 1/1.3 A Brachiosaurus is about 1.3 times as tall as a Stegosaurus is long. See side by side
  • 1/2.6 A tennis court is about 2.6 times as long as a Stegosaurus. See side by side

Factors compare the length (estimated) of a Stegosaurus with each object’s own main measurement (height for a human). Where a size varies, the factor is given as a range.

Notes on these figures

  • All sizes are estimates. The NHM Dino Directory gives no weight for Stegosaurus, so the headline mass is the AMNH figure.
  • Mass estimates differ widely: AMNH gives 2,720 kg, while the NHM's well-preserved young adult was estimated at about 1,600 kg.
  • The 9 m headline is at the large end; Britannica says Stegosaurus usually grew to about 6.5 m.

Sources

  1. Natural History Museum, London, Stegosaurus (Dino Directory). Accessed 25 September 2026.
  2. Natural History Museum, London, Weight of the world's most complete Stegosaurus revealed. Accessed 25 September 2026.
  3. American Museum of Natural History, Stegosaurus stenops (OLogy card 017). Accessed 25 September 2026.
  4. Encyclopaedia Britannica, Stegosaurus. Accessed 25 September 2026.

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