PHYS 2211 Module 1.5

Estimates and Fermi Calculations

Recommended Reading

1.5 Estimates and Fermi Calculations

Learning Objectives

By the end of this section, you will be able to:

  • Estimate the values of physical quantities.

Estimation means using prior experience and sound physical reasoning to arrive at a rough idea of a quantity’s value. Because the process of determining a reliable approximation usually involves the identification of correct physical principles and a good guess about the relevant variables, estimating is very useful in developing physical intuition.


Practice 1.5.1
Give an estimate of the number of steps in the stairway of a ten-story building.
(a) 101
(b) 102
(c) 103
(d) 104
Practice 1.5.2
Very roughly, how thick is one page of a textbook?
(a) 1 × 10-5 m
(b) 1 × 10-4 m
(c) 1 × 10-3 m
(d) 1 × 10-2 m
(e) 1 × 10-1 m


Consider how you would answer this question. Then bring this to class for a group discussion.

Estimate how many tennis balls it would take to fill our classroom (or any room you happen to be in).