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Activity: how big is your brain?

Activity to understand the scale of the brain using sugar grains
cartoon of a bag of sugar, brain and neuron
© Gareth Evans and Sangeeta Chawla

If a neuron was the size of a grain of sugar…

The purpose of this activity is to get a perspective on the complexity and scale of the brain. You have learned that the average human brain contains 86 billion neurons. A 1 kg bag of sugar is a reasonable approximation to the average size and weight of a human brain. Imagine if each neuron was the size of a grain of sugar. How many bags of sugar would be needed to make a human brain?


  • Calculator
  • Pen and paper
  • Access to the internet
  1. Your first task is to work out how many sugar grains there are in a 1 kg bag of granulated sugar. To save you performing the agonising task of weighing sugar grains, we have worked out that a grain of sugar weighs 50 µg (micrograms).
  2. Your next task is to work out how many bags of sugar you would need to accumulate 86 billion grains of sugar.

    The answer to this calculation will blow your mind, thinking about how many neurons there are in the brain!

  3. When you consider that each neuron has at least 1000 synaptic connections with other neurons, can you work out approximately how many synapses there are in the human brain? This is another bewildering number!

    There are data available on the number of neurons in the brains of different organisms. As you might expect, the number of neurons and hence computational power has increased through evolution.

  4. Can you find an organism that has a brain with approximately the same number of neurons as grains in just one bag of sugar?
  5. What is the smallest nervous system (least number of neurons) you can find?
© Gareth Evans and Sangeeta Chawla
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The Biology of Bugs, Brains, and Beasts

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