What is the fermi problem-solving strategy?

Benjamin Landry
3 min readDec 29, 2020

What is a fermi problem and what does it mean to fermi-ize it?

A fermi problem is a category of problems that require estimations and assumptions to solve. It tends to be creative or out-of-the-box questions. To fermi-ize a problem involves solving a problem with the fermi problem-solving strategy. The essence is to breakdown a large and broad question into its smallest elements. At which time, each element would be solved for. Then, all the elements would be accumulated to produce a conclusion.

When I discovered this technique it radically changes my ability to resolve creative problems my mind would invent as a potential project. Now that I use it, I think about problems differently. I am able to focus on tangible elements that are solvable, instead of using only my gut feeling assumptions.

How to pose a good fermi question?

The goal of the question should be clear and the outcome should be a quantity. The questions should not be impossible, unknowable and unpredictable. For example, “who will win the Super Bowl in 2050?” or “will the stock market go up or down tomorrow?”

Good Fermi Example are:

  • How many times could you say the alphabet in 24 hours?
  • How many ping pong balls would it take to fill the classroom?

How do you solve a fermi problem?

Once you have determined the problem that you want to solve. Follow the following process:

  • Write the key terms that regards the problem
  • Write the smallest questions needed to solve the problem
  • Write assumptions made and facts found, regarding the smallest questions
  • This step involves researching for information, to solve the smallest questions
  • Write and perform calculations using the facts & assumptions
  • Generate a point form conclusion that provides an answer to the original problem

What value does fermizing a problem provide?

Fermizing a problem allows anyone to solve problems where you have little or no data. It provides a sequential approach for anyone to solve seemingly unsolvable problems. It provides a good base estimate for many types of problems. It is an excellent method to solve out-of-the-box questions or creative questions.

When should you use it?

This problem solving strategy is used frequently with entrepreneurs, inventors, scientists, engineers, and the general population. I believe everyone should know how to use it, and individually decide when to use it.


Let me know if you will consider using the fermi problem solving strategy.


An example of solving a Fermi Problem

How much carbon dioxide was produced in the building of the 3 gorges dam (i.e. a typical large hydroelectric dam)?

Key terms

  • Dams, concrete, cement

Facts found / assumptions made

  • Dams are composed of concrete and steel
  • 1 unit of Concrete is composed of 63% CaO
  • Every production unit of Ca0 from CaCO3, produces 1 unit of CO2
  • Size of Three Gorge Dam is: 181m * 2335m * (40 + 115)/ 2 m = 33 million meters cubed
  • Concrete amount: 28 million meters cubed
  • Steel amount: 46300 metric tons


  • Amount of CO2 = 28 million meters cubed of concrete * 0.63 [concrete to CaO] * 1 CO2 / 1 CaO

= 17 million meters cubed of CO2


Therefore, 17 million meters cubed of CO2 is produced from the construction of the Three Gorge Dam, by concrete

Additional Notes

  • 900 kg of CO2 is emitted for every ton of cement
  • 1 ton = 907 kg



Benjamin Landry

I spend my time dreaming about food, watching fictional characters go through adventures, and think of creative ideas to improve the future.